Show proper error message when wrong command provided

Acloud limits the command to "-h, --version, setup, create, list, delete,
reconnect, pull, restart, hostcleanup". If the command is not in the
list, show the acloud supports commands to user.

Bug: 284428054
Test: acloud-dev --local-image
Change-Id: Id70c4550761085d3d2be576e9116b1f0b6e3a563
1 file changed