Install ceilometerclient to fix nova notfication_driver errors

Fixes error messages like:

2013-07-11 10:07:19.256 ERROR nova.openstack.common.notifier.api [req-65c5c212-63d5-4376-b755-941bea66e828 526abc01f1f2485198c3341957c3c22f 4cd1601e28f44a2da9727a518ac1198b] Failed to load notifier ceilometer.co
mpute.nova_notifier. These notifications will not be sent.
2013-07-11 10:07:19.256 16087 TRACE nova.openstack.common.notifier.api Traceback (most recent call last):
2013-07-11 10:07:19.256 16087 TRACE nova.openstack.common.notifier.api   File "/usr/lib64/python2.6/site-packages/nova/openstack/common/notifier/api.py", line 169, in add_driver
2013-07-11 10:07:19.256 16087 TRACE nova.openstack.common.notifier.api     driver = importutils.import_module(notification_driver)
2013-07-11 10:07:19.256 16087 TRACE nova.openstack.common.notifier.api   File "/usr/lib64/python2.6/site-packages/nova/openstack/common/importutils.py", line 58, in import_module
2013-07-11 10:07:19.256 16087 TRACE nova.openstack.common.notifier.api     __import__(import_str)
2013-07-11 10:07:19.256 16087 TRACE nova.openstack.common.notifier.api ImportError: No module named ceilometer.compute.nova_notifier
2013-07-11 10:07:19.256 16087 TRACE nova.openstack.common.notifier.api