Dgoodwin/container mode

Allow yum plugin to actually generate redhat.repo in a situation where we have no identity cert, but do have entitlement certs. Disable messaging to tell use to register in this scenario.

subscription-manager CLI completely disabled if in container mode. There is an argument to be made that perhaps some commands might be useful (list --consumed and --installed), but given the goal of not having subscription-manager installed at all (we plan to extract a small library for just yum plugin and repo generation bits), it's probably best to shut it down entirely lest anyone get used to it being there.