Use Token Clients from the client factory

Token clients were still instantiated separately in clients.py.
For consistency we should use the token clients from the client
factory in service_clients.

Since token clients have a very different interface, they will
ignore most of the parameters passed to them, and they need
an auth_url to be specified, as they don't use an auth_provider
like all other clients. When token clients call __init__ on
super(), they force service, region and auth_provider to None, so
we must ensure that they are not in the kwargs passed through
to super as well.

Documenting this in the ServiceClients class docstring as well
so that consumers know how instantiate a token client from it
in case they need to.

Change-Id: I95a3fd1a8859e807e04717eae82bf01f0d9a2085
diff --git a/tempest/clients.py b/tempest/clients.py
index 4092852..ec53bf3 100644
--- a/tempest/clients.py
+++ b/tempest/clients.py
@@ -19,7 +19,6 @@
 from tempest.lib import auth
 from tempest.lib import exceptions as lib_exc
 from tempest.lib.services import clients
-from tempest.lib.services import identity
 from tempest.services import object_storage
 from tempest.services import orchestration
 
@@ -236,15 +235,15 @@
         # API version is marked as enabled
         if CONF.identity_feature_enabled.api_v2:
             if CONF.identity.uri:
-                self.token_client = identity.v2.TokenClient(
-                    CONF.identity.uri, **self.default_params)
+                self.token_client = self.identity_v2.TokenClient(
+                    auth_url=CONF.identity.uri)
             else:
                 msg = 'Identity v2 API enabled, but no identity.uri set'
                 raise lib_exc.InvalidConfiguration(msg)
         if CONF.identity_feature_enabled.api_v3:
             if CONF.identity.uri_v3:
-                self.token_v3_client = identity.v3.V3TokenClient(
-                    CONF.identity.uri_v3, **self.default_params)
+                self.token_v3_client = self.identity_v3.V3TokenClient(
+                    auth_url=CONF.identity.uri_v3)
             else:
                 msg = 'Identity v3 API enabled, but no identity.uri_v3 set'
                 raise lib_exc.InvalidConfiguration(msg)