Allow cnames to not conflict with themselves when changing container

[murrown]

It looks like the Travis error is unrelated to this pull request. I ran the tests locally and they all passed.

You are using pip version 6.0.7, however version 7.0.3 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
...
Collecting Babel==0.9.6 (from -r requirements/prod.txt (line 18))
  Downloading Babel-0.9.6.tar.gz (1.8MB)
    51% |################                | 929kB 19.4MB/s eta 0:00:01  Exception:
  Traceback (most recent call last):
...
  error: [Errno 104] Connection reset by peer
The command "pip install -r requirements/dev.txt" failed and exited with 2 during .
Your build has been stopped.

[akeym]

works