Stop basic_setup from raising an exception

The ceilometer setup script is a setup script not a test so it
should not raise a skip exception if it is not needed. The fact
that it does is my fault and was implemented on my recommendation.

zaza/openstack/charm_tests/ceilometer/setup.py

@@ -17,7 +17,6 @@
 """Code for configuring Ceilometer."""
 
 import logging
-import unittest
 import zaza.model as zaza_model
 import zaza.openstack.utilities.openstack as openstack_utils
 
@@ -32,8 +31,9 @@ def basic_setup():
     xenial_pike = openstack_utils.get_os_release('xenial_pike')
 
     if current_release < xenial_pike:
-        raise unittest.SkipTest('Skipping ceilometer-upgrade as it is not '
-                                'supported before Pike')
+        logging.info(
+            'Skipping ceilometer-upgrade as it is not supported before Pike')
+        return
 
     logging.debug('Checking ceilometer-upgrade')