Fix consistency groups test credentials

This patch fixes the test for consistency groups, changing it to an admin
test in order to perform required operations.

Change-Id: I5f7fd8d62ace7d880a27697cf2b15fbb13cde706
Depends-On: I8bdfc31bb2baeabe1d599ea6e9be3c473531f8b6
Closes-Bug: #1789944
diff --git a/cinder_tempest_plugin/api/volume/base.py b/cinder_tempest_plugin/api/volume/base.py
index b3765e0..d1e71ef 100644
--- a/cinder_tempest_plugin/api/volume/base.py
+++ b/cinder_tempest_plugin/api/volume/base.py
@@ -168,3 +168,15 @@
                         self.os_primary.servers_client.delete_server,
                         body['id'])
         return body
+
+
+class BaseVolumeAdminTest(BaseVolumeTest):
+    """Base test case class for all Volume Admin API tests."""
+
+    credentials = ['primary', 'admin']
+
+    @classmethod
+    def setup_clients(cls):
+        super(BaseVolumeAdminTest, cls).setup_clients()
+
+        cls.admin_volume_types_client = cls.os_admin.volume_types_client_latest