vapp returns false if power action returns bad_request

Fixed issues - where fog models throw exception if it fails to
execute power action on vapp. This happens because the current state
of vapp does not let user execute the action.
e.g If vapp is in power_off state, it throw bad_request if user executes power_off, suspend,reboot or shutdown action.

In such case we should return false instead of throwing exception. Also printing the error message.

@nosborn : Could you please take a look?