When Simplified Content Access is enabled for a subscription,
the portal can be used with an activation key AND repositories.

So this patch adds a new parameter, rhsm_simplified_content_access
(False by default for backward compatibility).
When set to True, we'll allow the "Configure repository subscriptions"
task to be run without any warning since both the rhsm_repos and
rhsm_activation_key usually mutually exclusive, now work together when
simplified content access is enabled.

Change-Id: I4ffa344956572ebcd5a432fe41b86eb682f8d2a3