use sam when registering sat6+

Use SAM/subscription-manager instead of legacy registration for
new Satellite.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1067355
Change-Id: I9906ef0e605c3936ba4d1cf7b80e8a83e5863d19
Signed-off-by: Joey Boggs <jboggs@redhat.com>