Merged some commits in my docker role

After some work on the docker ansible role, I merged my own commits from dev branch to master.

The list commits can be found here with comments in the git log detailing the changes.

Here's the Gitlab.com link for commit history.

Of course, I wouldn't recommend using my own role for anyone but myself, instead I would point people to Jeff Geerling's docker role on Github.

His role has a lot more work, commits and features added.