Ensure staged rollback status is logged on boot

In the cases that a logging parent cannot be found for any packages
in a rollback, the watchdog event should still be logged. Ensure
that the state of a rollback is captured on boot by removing the
condition of only saving a rollback id if there is a logging package,
and by adding a symbolic null package to the list of logging packages
on boot if none were found. Expand tests to verify.

Bug: 149957011
Test: atest StagedRollbackTest
Test: atest NetworkStagedRollbackTest
Change-Id: I56f8afb6730e59fbe67ea8747e0da3aca19a0d8a