Define 4 identity v2 clients as libraries

- roles_client
- services_client
- tenants_client
- users_client
of identity v2 services are stable and good interface to
migrate those in libraries interfaces.

neutron tempest tests and other CI use below service clients
from tempest path so keeping those temporarily in tempest also
otherwise it will break their gate.
These service clients  will be removed from tempest path once
those interface are released n lib and fixed in neutron side etc.
- roles_client
- tenants_client
- users_client

Partially implements blueprint consistent-service-method-names

Change-Id: I3c09396f36a82d484de226cfe27848b6916cb636
diff --git a/tempest/tests/common/test_dynamic_creds.py b/tempest/tests/common/test_dynamic_creds.py
index 7a8637f..b7cc05d 100644
--- a/tempest/tests/common/test_dynamic_creds.py
+++ b/tempest/tests/common/test_dynamic_creds.py
@@ -22,14 +22,14 @@
 from tempest import exceptions
 from tempest.lib.common import rest_client
 from tempest.lib import exceptions as lib_exc
+from tempest.lib.services.identity.v2 import roles_client as v2_roles_client
+from tempest.lib.services.identity.v2 import tenants_client as \
+    v2_tenants_client
 from tempest.lib.services.identity.v2 import token_client as v2_token_client
+from tempest.lib.services.identity.v2 import users_client as v2_users_client
 from tempest.lib.services.identity.v3 import token_client as v3_token_client
 from tempest.lib.services.network import routers_client
 from tempest.services.identity.v2.json import identity_client as v2_iden_client
-from tempest.services.identity.v2.json import roles_client as v2_roles_client
-from tempest.services.identity.v2.json import tenants_client as \
-    v2_tenants_client
-from tempest.services.identity.v2.json import users_client as v2_users_client
 from tempest.services.identity.v3.json import domains_client
 from tempest.services.identity.v3.json import identity_client as v3_iden_client
 from tempest.services.identity.v3.json import projects_client as \