Tempest: Adopt keystone api v3 for tests

Adopt v3 for the few tests that require v3 endpoint

Change-Id: I2bcc9ac2949f5f4d7e22a83f3839b97a775763db
diff --git a/neutron/tests/tempest/api/base.py b/neutron/tests/tempest/api/base.py
index d0b8382..84746fb 100644
--- a/neutron/tests/tempest/api/base.py
+++ b/neutron/tests/tempest/api/base.py
@@ -430,6 +430,7 @@
         super(BaseAdminNetworkTest, cls).setup_clients()
         cls.admin_client = cls.os_adm.network_client
         cls.identity_admin_client = cls.os_adm.tenants_client
+        cls.identity_admin_clientv3 = cls.os_admin.projects_client
 
     @classmethod
     def create_metering_label(cls, name, description):