Drop admin_role CONF dependency from cred provider

Cred providers depend on the admin_role which is read from CONF.
Adding that as a new mandatory parameter in preparation to
migration to tempest-lib.

Change-Id: Ic8ae2d36978635c9c9bade23cfef737dc3fb44b1
Partially-implements: bp tempest-library
diff --git a/tempest/tests/test_dynamic_creds.py b/tempest/tests/test_dynamic_creds.py
index 08b2ab6..59a5523 100644
--- a/tempest/tests/test_dynamic_creds.py
+++ b/tempest/tests/test_dynamic_creds.py
@@ -33,7 +33,8 @@
 class TestDynamicCredentialProvider(base.TestCase):
 
     fixed_params = {'name': 'test class',
-                    'identity_version': 'v2'}
+                    'identity_version': 'v2',
+                    'admin_role': 'admin'}
 
     def setUp(self):
         super(TestDynamicCredentialProvider, self).setUp()