add arg -confdir

[vcptr]

A common way of reading multiple config file is to scan a directory and read config files inside by the order of their names. This PR make multiple config feature more practical by adding -confdir arg.

Adds

• v2ray arg: -confdir - A dir with multiple json config
• env v2ray.location.confdir or V2RAY_LOCATION_CONFDIR
• more details logs about config during program start.

Examples

When use with multiple config, lines after <v2ctl message> will tell the order of how config file is processed.

$ ./v2ray -confdir ./vjson
V2Ray 4.22.0 (V2Fly, a community-driven edition of V2Ray.) Custom
A unified platform for anti-censorship.
2019/12/31 13:45:49 [Info] v2ray.com/core/common/platform/ctlcmd: <v2ctl message> 
v2ctl> Read config:  vjson/01dohipm.json
v2ctl> Read config:  vjson/02doh.json
v2ctl> Read config:  vjson/03out.json
v2ctl> [ vjson/03out.json ] updated outbound with tag:  proxy
2019/12/31 13:45:49 [Debug] v2ray.com/core/app/log: Logger started
...
2019/12/31 13:45:49 [Warning] v2ray.com/core: V2Ray 4.22.0 started

So as using env, logs how the config is speculated. (... Using confdir from env)

$ env V2RAY_LOCATION_CONFDIR=/home/ubuntu/vjson ./v2ray 
V2Ray 4.22.0 (V2Fly, a community-driven edition of V2Ray.) Custom
A unified platform for anti-censorship.
2019/12/31 13:48:02 Using confdir from env:  /home/ubuntu/vjson
2019/12/31 13:48:02 [Info] v2ray.com/core/common/platform/ctlcmd: <v2ctl message> 
v2ctl> Read config:  /home/ubuntu/vjson/01dohipm.json
v2ctl> Read config:  /home/ubuntu/vjson/02doh.json
v2ctl> Read config:  /home/ubuntu/vjson/03out.json
v2ctl> [ /home/ubuntu/vjson/03out.json ] updated outbound with tag:  proxy
2019/12/31 13:48:02 [Warning] v2ray.com/core: V2Ray 4.22.0 started

If there's problems in config file, the error message is easy to read

$ ./v2ray 
V2Ray 4.22.0 (V2Fly, a community-driven edition of V2Ray.) Custom
A unified platform for anti-censorship.
2019/12/31 14:00:29 Using default config:  /home/ubuntu/config.json
main: failed to read config files: [/home/ubuntu/config.json] > v2ray.com/core/main/json: failed to execute v2ctl to convert config file. > v2ray.com/core/common/platform/ctlcmd: failed to execute v2ctl: 
v2ctl> Read config:  /home/ubuntu/config.json
v2ctl> v2ray.com/core/infra/conf/serial: failed to read config file at line 15 char 5 > invalid character ',' looking for beginning of object key string > exit status 1