This does a couple of things:
* Loads the Identity client module in the same manner as the other
'base' clients (where 'base' == 'included in the OSC repo')
* Changes the entry point group name for the base clients to
'openstack.cli.base'. The extension group name remains the same.
* Loads the base modules first followed by the extension modules.
This load order ensures that the extension module commands are all
loaded _after_ the base commands, allowing extensions to now override
the base commands.
Change-Id: I4b9ca7f1df6eb8bbe8e3f663f3065c2ed80ce20b
1ab38679b6