foremain-maintain should validate whether satellite is self registered or not, before starting upgrade.
Description of problem:
From satellite v 6.3 onwards, we are not supporting self-registered satellite server, reference  and 
The foreman-maintain should add this check and notify the users accordingly in pre-upgrade check and ask customer follow upgrade steps for disconnected satellite server.
It will be nice if we could point the KCS / Doc link for the disconnected upgrade.
Version-Release number of selected component (if applicable):
Red Hat Satellite 6.3 Upgrade