Allow "bin/repository thaw --demote" to demote an entire service, not just a single device

Summary: Ref T13222. See PHI992. If you lose an entire cluster, you may want to aggressively demote it out of existence. You currently need to xargs your way through this. Allow --demote <service>, which demotes all devices in a service.

Test Plan: Demoted with --demote <device> and --demote <service>. Hit the --promote service error.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13222

Differential Revision: https://secure.phabricator.com/D19850