Heat: use first_address instead of first_private_address

first_private_address no longer exists in OS::Nova::Server
as it was a misconceived feature.

Change-Id: Id1a0eeca1bf3b57c27e6b93ae64e11d3de9b771e
Related-Bug: #1228929
Add test for admin deleting servers of others

Administrator can delete servers of other users.

Change-Id: I08a9de69dae18a743b872ceb7b070400c1ac39a8
Merge "Add test for admin deleting servers of others"
Merge "Heat: use first_address instead of first_private_address"