convert vppdev.sh to Go binary

[aritrbas]

[CALICOVPP-9] This converts vppdev.sh to a Go binary to leverage Golang APIs.

Placed it under an "util" folder.
"make util" creates the "calivppctl" Go executable under util/bin/ directory.

Usage:

• calivppctl vppctl [NODENAME] - Get a vppctl shell on a specific node
• calivppctl log [-f] [-vpp|-agent|-felix] [NODENAME] - Get the logs of vpp (dataplane) or agent (controlplane) or felix daemon
• calivppctl clear - Clear vpp internal stats
• calivppctl export - Create an archive with vpp & k8 system state for debugging.
• calivppctl exportnode [NODENAME] - Create an archive with vpp & k8 system state for a specific node.
• calivppctl gdb - Attach a gdb to the running vpp on the current machine
• calivppctl sh [vpp|agent] [NODENAME] - Get a shell in vpp (dataplane) or agent (controlplane) container

[sknat]

Thanks a lot @aritrbas ! That's neat !
Added a few comments inline, some are more debatable (e.g. I don't think we need to remove every single CLI commands for the V0) but I think we'll eventually want to converge there.

Happy to discuss this with you