Local copy of 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

Maintain a local copy of the base class, taken from Tempest with head of
master at c5f1064759fe6c75a4bc5dc251ed1661845936cb.

Change-Id: Idfa5ebe18c794c51e406156fb120d128478d4f1e

watcher_tempest_plugin/tests/scenario/base.py

@@ -25,9 +25,9 @@ from oslo_log import log
 from tempest import config
 from tempest import exceptions
 from tempest.lib.common.utils import data_utils
-from tempest.scenario import manager
 
 from watcher_tempest_plugin import infra_optim_clients as clients
+from watcher_tempest_plugin.tests.scenario import manager
 
 LOG = log.getLogger(__name__)
 CONF = config.CONF