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
I did enable forwarding in the DNS charms that needs to go with it. I forward to local cloud dns and 8.8.8.8 which is NOT always reachable.