Add tests for list and description for Server commands:
- Check server commands in main help message.
- Check list of server-related commands only.
Commands:
server add security group,
server add volume,
server create,
server delete,
server dump create,
server image create,
server list,
server lock,
server migrate,
server pause,
server reboot,
server rebuild,
server remove security group,
server remove volume,
server rescue,
server resize,
server resume,
server set,
server shelve,
server show,
server ssh,
server start,
server stop,
server suspend,
server unlock,
server unpause,
server unrescue,
server unset,
server unshelve.
Change-Id: Ib4bf9ab0264fb482d36cf5688c0f939bcd2cb6d8
