Send backup success notification to background apps as well

When the backup manager is configured to notify one or more apps of
successful backups, the notifications should be sent to apps that are
currently stopped as well.

Bug: 63885845
Test: cts-tradefed run cts-dev --module CtsBackupHostTestCase
Change-Id: I7086aee105229e0f8db4b1ec26639d53a4e0af37