command.Command and command.Showone are base classes implemented
in cliff framework. Showone extends Command to allow take_action()
to return data to be formatted using a user-selectable formatter.
Most of the classes which are extended from Command in
openstackclient/identity/v3/ in some cases return data or return
nothing where it is not necessary, this commit fixes most of them.
Change-Id: I84c72ea4d6680f8bdbef5449316dd9a8af8c8286
Closes-Bug: 1550892
3d7430463c