@admin decorator switched to use require_roles
@admin decorator switched to use require_roles

The decorator was using a function almost identical to the require
roles function, already being used by the mod_or_admin decorator.

The only differences was the hardcoding of the role it was looking
for rather than being a part of the set given.

Change-Id: I67b3555d60aa7446bba8abebf2b07fd80e18e38d
catalyst/stacktask