Fix problem with using latest version of python-novaclient

Fix problem of using the latest version of python-novaclient
on the Puppetmaster.  The latest version is version 2.19 which
is incompatible with the HP Cloud version 13.5 infrastructure.
This fix will pin the version of python-novaclient to 2.18.

Change-Id: I3ff58a6fe70bcac47ec94351e7fc56a75aefc4d2
Closes-Bug: #1341787
Merge "Fix problem with using latest version of python-novaclient"