Disable all repos during rhel registration

Some accounts get repos automatically enabled when the system is
registered, which is a problem because some of these repos pull in
things we don't want like early beta versions of software.  Since
a full list of desired repos is supposed to be included as part of
the registration config, let's just disable all repos to start with
to ensure we have a clean repo configuration.

I'm not sure whether satellite has the same problem (I would think
not, since satellite should only be providing the desired repos),
so I'm only making this change for portal registration.

Change-Id: I052080352e8b1c9b985e42d91a6c42b3258b0b11
Closes-Bug: 1629922
(cherry picked from commit 2b06ed8adc)

extraconfig/pre_deploy/rhel-registration/scripts/rhel-registration

@@ -116,6 +116,7 @@ case "${REG_METHOD:-}" in
         if [ -z "${REG_AUTO_ATTACH:-}" -a -z "${REG_ACTIVATION_KEY:-}" ]; then
             subscription-manager attach $attach_opts
         fi
+        subscription-manager repos --disable '*'
         subscription-manager $repos
         ;;
     satellite)