Define v2 identity_client as library

Migrate identity v2 API identity_client to tempest.lib and implement
unit test for the service clients.
Partially implements blueprint consistent-service-method-names

Change-Id: I243af8583d5b497f7df3ce5dd39fe1dbd3ce0eca
diff --git a/tempest/tests/common/test_dynamic_creds.py b/tempest/tests/common/test_dynamic_creds.py
index e7b9a4c..8c74d9c 100644
--- a/tempest/tests/common/test_dynamic_creds.py
+++ b/tempest/tests/common/test_dynamic_creds.py
@@ -22,6 +22,7 @@
 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 identity_client as v2_iden_client
 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
@@ -31,7 +32,6 @@
     v3_projects_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.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 roles_client as v3_roles_client