Parallelize the deployment to slaves

Currently clusterrunner deploy on ~30 machines take a minute and a half.

This commit makes that signficantly faster, and no longer proportionally linear with the number of deployed slaves.
Stopping the services are synchronous (because we want to make sure that the service stops, and also there is no possibility of hanging because the 'stop' subcommand is not run as a background/daemon process).

The starting of the services, which is immediately below these lines, is not done using starmap for the reasons I just listed above.