Add compute notifications tests for ceilometer

Added ceilometer test for measurements:
instance, instance:<type>, memory, vcpus, disk.root.size,
disk.ephemeral.size

Change-Id: Ic99229d38f17cd81e147d86031aca75c13171057
Partially implements: blueprint add-basic-ceilometer-tests
diff --git a/tempest/config.py b/tempest/config.py
index f9be90d..c8306f7 100644
--- a/tempest/config.py
+++ b/tempest/config.py
@@ -633,6 +633,10 @@
                choices=['public', 'admin', 'internal',
                         'publicURL', 'adminURL', 'internalURL'],
                help="The endpoint type to use for the telemetry service."),
+    cfg.BoolOpt('too_slow_to_test',
+                default=True,
+                help="This variable is used as flag to enable "
+                     "notification tests")
 ]