Last modifications to work on OpenStack

As been tested with this : http://code.launchpad.net/~thomnico/charms/precise/dns/openstack-support

Worked on both EC2 and private openstack. Tested with sipml5 charm in the charmstore.

Please comment
As on the other trail (https://code.launchpad.net/~thomnico/charms/precise/clearwater-sprout/openstack-support/+merge/233709), I'm keen to understand why this chunk is required.