Add support for new docker restart policies

Docker deprecated the "-r" switch for the docker daemon.
Since docker 1.2 every container can now have it's own restart policy.

Module restart_policy option defaults are the same as the docker command defaults.
Needs docker-py >= 0.5.0.
Settings get ignored when used with a lower docker-py version. Tested it with docker-py 0.3.2. 
I just wanted to stick to the already used convention of the module.
_dns_ and _volumes_from_ is implemented exactly the same way in the if-block above.

If ansible prefers an error on module version mismatches (like I do), then I think this should be fixed for the whole module in a separate PR.
Changing the habits from option to option makes the modules' behaviour somewhat unpredictable.