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.
Ideally, we wouldn't need this stanza anyway. It's just to try a network connection to the server before
we get into the bowels. Perhaps with some exception handling cleanup, we could ditch it. But sans that,
this seems reasonable.