SubscriptionManager#addOnSubscriptionsChangedListener can fail to
register a listener if the TELEPHONY_REGISTRY system service is not up.
Currently this is just silently ignored.
Adding a callback method on the listener to notify the registrant that the
listener failed to be registered, and adding exponential backoff code in
TelecomAccountRegistry to retry registration.
Test: Manual; edited code in Subscriptionmanager to fail the first attempts
to add a listener for TelecomAccountRegistry. Verified the backoff took
place and registration still occurred for the listener.
Test: Tried to write a mockito test but gave up because this code has
far too many intertwined dependencies and is not inherently testable
Fixes: 152217039
Change-Id: Icf3133cdeca526979cb621f29659b880127b680a
cf2cd8dcd8