Let debug builds set SubscriptionPlan owners.

Examine system property to decide if a test app should be granted
the ability to manage SubscriptionPlan details for a specific subId.

This doesn't give the testing app any access to existing plans
defined by other carrier apps, it only allows the testing app to
provide plans for testing purposes.  Purposefully ignored on
end-user builds.

Test: builds, boots
Bug: 73173096
Change-Id: I926ec0f88b7c2c282a1ec4410eaab92e1e1090dd