Add support for domains when deleting identity v3 resources

Currently, only deleting via IDs is possible for groups, projects
and users.
We should have an optional --domain argument that allows for
a name to be specified for the resource. (Since these are all
namespaced by domains).

Change-Id: I18ace3db85a3969f0b97678d432d6f8368baa9cd
Merge "Add support for domains when deleting identity v3 resources"