[Part 2] Made Admin CLI return proper code to shell

[shuklanirdesh82]

#1464 is fixing partially Admin CLI return code .. This issue is tracking the remaining work.

Some more reference from #1464 (comment)

Partially addresses #1411

CLI code used to print error message and exit, without passing proper code to shell.
This PR fixes that.
There may still be some functions which do not return proper status , but at least this fixes the framework

Functions which do not return proper code: example.
set_vol_opts() should return None on success and return "err msg" on error. Currently it prints stuff and always returns success. A quick review of CLI code is needed to make sure all return proper code.