Return codes for "one-shot" invocation mode

[khosrow]

Provide useful return codes when the command is invoked in one-shot. i.e.:
lvsm real enable my-frontend http

This can help if people want to automate tasks with lvsm.

Some commands may not lend themselves to meaningful return codes, while others may. In that case those ambiguous commands should just return 0.

Some candidates for proper return codes are:

• real enable
• real disable
• restart <modules>