[google|dns] Add initial support for Google Cloud DNS.

- some common plumbing
- requests for creating, deleting and listing managed zones, with tests
added ready? for sshable
removing the depreciation warning when calling key_pair from an aws server
Merge remote-tracking branch 'upstream/master'
[aws|dns] mark mocked tests as pending
Merge pull request #3104 from techlunacy/master

updating the key_pair method call from the aws server model
Merge pull request #3103 from dennybaa/master

added ready? for sshable
Merge pull request #3094 from porridge/google-dns

[google|dns] Add initial support for Google Cloud DNS.