Stop depending on scenario test base class

The scenario tests base class from Tempest is not a stable interface
and it's going to be refactored on Tempest side, as notified in

http://lists.openstack.org/pipermail/openstack-dev/2017-February/112938.html

Stop using that class since there's nothing in it used by horizon
scenario test.

Change-Id: I45ef6cef47a6a26e43612ffc6cb8851d19372712
diff --git a/tempest_horizon/tests/scenario/test_dashboard_basic_ops.py b/tempest_horizon/tests/scenario/test_dashboard_basic_ops.py
index 67ed227..e9f72d6 100644
--- a/tempest_horizon/tests/scenario/test_dashboard_basic_ops.py
+++ b/tempest_horizon/tests/scenario/test_dashboard_basic_ops.py
@@ -18,7 +18,7 @@
 
 from tempest import config
 from tempest.lib import decorators
-from tempest.scenario import manager
+from tempest import test
 
 import ssl
 import sys
@@ -59,7 +59,7 @@
             self.login = self._find_attr_value(attrs, 'action')
 
 
-class TestDashboardBasicOps(manager.ScenarioTest):
+class TestDashboardBasicOps(test.BaseTestCase):
 
     """The test suite for dashboard basic operations
 
@@ -70,6 +70,8 @@
     """
     opener = None
 
+    credentials = ['primary']
+
     @classmethod
     def skip_checks(cls):
         super(TestDashboardBasicOps, cls).skip_checks()