Clean up tenants created in test_users.py

Test_list_user_projects in test_users.py creates a tenant but
the tenant is not deleted at the end of the test.
This patch makes the tenant be deleted by adding addCleanup.

Fixes bug: 1179739

Change-Id: Ifc361363f74dcc43286e5fbdb582adf7f452dacc
diff --git a/tempest/tests/identity/admin/v3/test_users.py b/tempest/tests/identity/admin/v3/test_users.py
index 7118241..39b8ca1 100644
--- a/tempest/tests/identity/admin/v3/test_users.py
+++ b/tempest/tests/identity/admin/v3/test_users.py
@@ -74,6 +74,8 @@
         fetched_project_ids = list()
         _, u_project = self.v3_client.create_project(
             rand_name('project-'), description=rand_name('project-desc-'))
+        # Delete the Project at the end of this method
+        self.addCleanup(self.v3_client.delete_project, u_project['id'])
         #Create a user.
         u_name = rand_name('user-')
         u_desc = u_name + 'description'