Reload Group endpoint

[jwreagor]

During testing we uncovered a case where it would be handy to reload the TSG Nomad job/client without deleting/archiving the Group itself. This would allow the supervisor job running in Nomad to update to the latest client binary (and any other job attributes) w/o recreating the group to force the reload manually.

We could also hook this endpoint into a maintenance script that allows us to upgrade all clients running across the Nomad cluster. Get a list of all active groups and reload to deploy a new version of the TSG client. This might also help ensure that any jobs missing from Nomad are running as well.