Merge pull request #1266 from wallyworld/azure-services-for-env

Ensure only instances for this environment are used in azure operations

Instead of using the gwacl method ListPrefixedHostedServices() which can return services from other environments, we use out own method to return services for this environment.

Fixes: https://bugs.launchpad.net/juju-core/+bug/1398820

(Review request: http://reviews.vapour.ws/r/580/)