Docker network mode selection

Enables selection of the 'NetworkMode' option present in Docker

Granted this is nearly identical to of https://github.com/ansible/ansible/pull/7408 except after some testing the 0.3.2 checking seems important and I believe setting a default is required.

I believe adding might be important as without it, it doesn't seem docker-py sets it as the default, though I could be wrong. It was just another observation from testing.

This would close https://github.com/ansible/ansible/issues/7324

Cheers,

Pauly