Register Rollback user callbacks for added users

Rollback Manager gets notified when new user is added and then registers
broadcast receivers for that user. The broadcasts this user registers
for are the same as the ones the main user registers for on boot up.

Test: manual -
    1. Add new user to device.
    2. adb install RollbackTestAppAv1.apk
    3. adb install --user 10 --enable-rollback RollbackTestAppAv2.apk
    4. adb shell dumpsys rollback # observe available rollback
Test: atest RollbackTest
Test: atest StagedRollbackTest
Fixes: 133210559

Change-Id: If1666ebe46cb6e17818478b4b82a53369d7cedcc