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. 
It looks like this will silently ignore the restart_policy parameter if one of the docker-related versions is too old.  Is that correct?  Probably better to first check if restart_policy was specified.  If so, then return an error if the docker version is too old.