Update roles required for testing

This patch removes the hard-coded 'key-manager:service-admin' role from
the base test class because the role is not available in deployments
with the new Secure RBAC policies enabled.

There is only one test that still requires this role in the API quotas
tests, so we generate a dynamic user there and only use it in this
class.  This test is skipped when SRBAC is enabled.

Change-Id: I6fbfe43f821d9315e01d3bdfd6f5d4edf4e552b7
diff --git a/barbican_tempest_plugin/tests/api/base.py b/barbican_tempest_plugin/tests/api/base.py
index aa500f7..50ae662 100644
--- a/barbican_tempest_plugin/tests/api/base.py
+++ b/barbican_tempest_plugin/tests/api/base.py
@@ -61,8 +61,7 @@
                          api_version_utils.BaseMicroversionTest):
     """Base class for all api tests."""
 
-    # Why do I have to be an admin to create secrets? No idea...
-    credentials = ('admin', ['service_admin', 'key-manager:service-admin'])
+    credentials = ['project_admin']
     client_manager = clients.Clients
     created_objects = {}
 
@@ -88,8 +87,6 @@
         cls.secret_consumer_client = os.secret_v1_1.SecretConsumerClient()
         cls.secret_metadata_client = os.secret_v1.SecretMetadataClient()
         cls.version_client = os.secret_v1_1.VersionClient()
-
-        os = getattr(cls, 'os_roles_%s' % cls.credentials[1][0])
         cls.quota_client = os.secret_v1.QuotaClient()
 
     @classmethod