Add identity v3 project tags client

This PS adds ``project_tags_client`` to the identity v3
library. This feature enables the possibility of invoking
the following API actions:

    * update_project_tag
    * list_project_tags
    * update_all_project_tags
    * check_project_tag_existence
    * delete_project_tag
    * delete_all_project_tags

Change-Id: Iad6b3a88639bb4a0dc3aea5af2ba0162dfa19f96
Depends-On: Iec6b34c10ea1bd7103720c773b48ce130643115d
diff --git a/tempest/clients.py b/tempest/clients.py
index b06eafb..d75a712 100644
--- a/tempest/clients.py
+++ b/tempest/clients.py
@@ -197,6 +197,8 @@
         self.endpoint_groups_client = self.identity_v3.EndPointGroupsClient(
             **params_v3)
         self.catalog_client = self.identity_v3.CatalogClient(**params_v3)
+        self.project_tags_client = self.identity_v3.ProjectTagsClient(
+            **params_v3)
 
         # Token clients do not use the catalog. They only need default_params.
         # They read auth_url, so they should only be set if the corresponding