Add pprof to runc-shim

[henry118]

Adding pprof capability to containerd-runc-shim-v2.

This makes the shim to expose an additional debugging endpoint when running in DEBUG mode. And users can capture pprof data via ctr:

NAME:
   ctr shim pprof - Provide golang pprof outputs for containerd-shim

USAGE:
   ctr shim pprof command [command options] 

COMMANDS:
   block         Goroutine blocking profile
   goroutines    Dump goroutine stack dump
   heap          Dump heap profile
   profile       CPU profile
   threadcreate  Goroutine thread creating profile
   trace         Collect execution trace
   help, h       Shows a list of commands or help for one command

OPTIONS:
   --help, -h  Show help (default: false)

e.g. To capture the heap profile for the shim hosting container "test":

ctr shim --id test pprof heap >heap.prof 

[mxpv]

One minor nit, overall LGTM

[ZhangShuaiyi]

LGTM

[henry118]

@mxpv @dmcgowan @estesp Mind taking another look? Feel free to let me know anything required to merge this. Thanks :)

[dims]

LGTM

[estesp]

/test pull-containerd-node-e2e