Fix tunnel parsing exception handling.

[jshort]

Rather than using STFATAL and exiting, bubble up tunnel parsing exception to main and display the responsible option arg and print help menu so the user need not dig into /tmp/etclient-* to determine why et aborted.

Fixes #491

Testing:

 ❯ ./et -p abc localhost:8080 --macserver                                                                                                                                                                                     14:57:23  12.02.22
Exception: Argument ‘abc’ failed to parse


Remote shell for the busy and impatient
Usage:
  et [OPTION...] [user@]host[:port]

  Note that 'host' can be a hostname or ipv4 address with or without a port
  or an ipv6 address. If the ipv6 address is abbreviated with :: then it must
  be specified without a port (use -p,--port).

  -h, --help                 Print help
      --version              Print version
  -u, --username             Username
      --host arg             Remote host name
  -p, --port arg             Remote machine etserver port (default: 2022)
  -c, --command arg          Run command on connect
      --terminal-path arg    Path to etterminal on server side. Use if
                             etterminal is not on the system path.
  -t, --tunnel arg           Tunnel: Array of source:destination ports or
                             srcStart-srcEnd:dstStart-dstEnd (inclusive) port
                             ranges (e.g. 10080:80,10443:443,
                             10090-10092:8000-8002)
  -r, --reversetunnel arg    Reverse Tunnel: Array of source:destination
                             ports or srcStart-srcEnd:dstStart-dstEnd (inclusive)
                             port ranges
      --jumphost arg         jumphost between localhost and destination
      --jport arg            Jumphost machine port (default: 2022)
  -x, --kill-other-sessions  kill all old sessions belonging to the user
      --macserver            Set when connecting to an macOS server.  Sets
                             --terminal-path=/usr/local/bin/etterminal
  -v, --verbose arg          Enable verbose logging (default: 0)
  -k, --keepalive arg        Client keepalive duration in seconds
      --logtostdout          Write log to stdout
      --silent               Disable logging
  -N, --no-terminal          Do not create a terminal
  -f, --forward-ssh-agent    Forward ssh-agent socket
      --ssh-socket arg       The ssh-agent socket to forward
      --telemetry            Allow et to anonymously send errors to guide
                             future improvements (default: true)
      --serverfifo arg       If set, communicate to etserver on the matching
                             fifo name (default: )
      --ssh-option arg       Options to pass down to `ssh -o`


 ↵ 1  ⚙  jwshort@MAC-DESKTOP  ~/gitworkspaces/EternalTerminal/build   master ● ⍟2 
 ❯ ./et -t 6010 localhost:8080 --macserver                                                                                                                                                                                    14:57:34  12.02.22
Exception: Invalid tunnel argument: 6010


Remote shell for the busy and impatient
Usage:
  et [OPTION...] [user@]host[:port]

  Note that 'host' can be a hostname or ipv4 address with or without a port
  or an ipv6 address. If the ipv6 address is abbreviated with :: then it must
  be specified without a port (use -p,--port).

  -h, --help                 Print help
      --version              Print version
  -u, --username             Username
      --host arg             Remote host name
  -p, --port arg             Remote machine etserver port (default: 2022)
  -c, --command arg          Run command on connect
      --terminal-path arg    Path to etterminal on server side. Use if
                             etterminal is not on the system path.
  -t, --tunnel arg           Tunnel: Array of source:destination ports or
                             srcStart-srcEnd:dstStart-dstEnd (inclusive) port
                             ranges (e.g. 10080:80,10443:443,
                             10090-10092:8000-8002)
  -r, --reversetunnel arg    Reverse Tunnel: Array of source:destination
                             ports or srcStart-srcEnd:dstStart-dstEnd (inclusive)
                             port ranges
      --jumphost arg         jumphost between localhost and destination
      --jport arg            Jumphost machine port (default: 2022)
  -x, --kill-other-sessions  kill all old sessions belonging to the user
      --macserver            Set when connecting to an macOS server.  Sets
                             --terminal-path=/usr/local/bin/etterminal
  -v, --verbose arg          Enable verbose logging (default: 0)
  -k, --keepalive arg        Client keepalive duration in seconds
      --logtostdout          Write log to stdout
      --silent               Disable logging
  -N, --no-terminal          Do not create a terminal
  -f, --forward-ssh-agent    Forward ssh-agent socket
      --ssh-socket arg       The ssh-agent socket to forward
      --telemetry            Allow et to anonymously send errors to guide
                             future improvements (default: true)
      --serverfifo arg       If set, communicate to etserver on the matching
                             fifo name (default: )
      --ssh-option arg       Options to pass down to `ssh -o`


 ↵ 1  ⚙  jwshort@MAC-DESKTOP  ~/gitworkspaces/EternalTerminal/build   master ● ⍟2 
 ❯ ./et -t 6010:6000 localhost:8080 --macserver                                                                                                                                                                               14:57:55  12.02.22

####################################################################################
Welcome to your MacOS Desktop.
####################################################################################

[jshort]

Let me get some coverage for this. et::HandleTerminate is interfering with Catch2's REQUIRE_THROWS(...) but I should be able to work around it.

[codecov-commenter]

Codecov Report

Base: 70.75% // Head: 73.17% // Increases project coverage by +2.41% 🎉

Coverage data is based on head (aff4ad7) compared to base (91099f6).
Patch coverage: 95.38% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #550      +/-   ##
==========================================
+ Coverage   70.75%   73.17%   +2.41%     
==========================================
  Files          49       51       +2     
  Lines        3074     3094      +20     
==========================================
+ Hits         2175     2264      +89     
+ Misses        899      830      -69     

Impacted Files	Coverage Δ
src/terminal/TerminalClient.cpp	49.75% <ø> (+8.52%)	⬆️
src/base/TunnelUtils.cpp	93.18% <93.18%> (ø)
src/base/TunnelUtils.hpp	100.00% <100.00%> (ø)
test/TerminalTest.cpp	93.57% <100.00%> (+0.61%)	⬆️
src/terminal/TerminalServer.cpp	72.69% <0.00%> (-0.41%)	⬇️
src/base/Connection.cpp	88.69% <0.00%> (ø)
src/terminal/UserTerminalHandler.cpp	71.26% <0.00%> (+1.26%)	⬆️
src/base/SocketHandler.cpp	63.63% <0.00%> (+1.29%)	⬆️
src/terminal/UserJumphostHandler.cpp	64.80% <0.00%> (+3.19%)	⬆️
src/base/ClientConnection.cpp	77.27% <0.00%> (+3.63%)	⬆️
... and 2 more

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[jshort]

Ehhh, I want to move the tunnel parse logic and exception to a separate header/impl to get it out of TerminalClient.(hpp|cpp).