<oo-admin-yum-validator> Bug 1031081, Replace y-c-m advice with "by hand" advice

https://bugzilla.redhat.com/show_bug.cgi?id=1031081

Replaced `yum-config-manager` dependent advice for RHSM with by-hand
instructions, since the `--setopt` argument in `yum-config-manager`
doesn't work with dotted repoids. The `--enable` and `--disable` args
still work for dotted repoids, so that advice remains for the
plain-old-yum case