Correct cache use in SubscriptionManager

Bug: 234632427

Change the SubscriptionManager caches so that error conditions
(RemoteException, null ISub, TimeoutException) do not generate values
in the cache.  Instead, these error conditions are handled above the
cache.

Test: atest
 * SubscriptionControllerTest
 * android.telephony.cts.SubscriptionManagerTest
Change-Id: I758a4636a49e7889cfd08b613e90cb09411fc8ab