Update SCC migration plugin to support groups

[dymurray]

Alex recently added support for the plugin to detect when SCCs are being used by specific SAs, and to automatically add them to the backup. This was a great first step, now we need to update the plugin to have some more intelligence for the case of when the SCC does not list a service account by name, but rather via group.

See https://blog.openshift.com/understanding-service-accounts-sccs/ for more information on SCCs and groups vs users.