Fix RollbackPackageHealthObserver for rollback-all

Making RollbackPackageHealthObserver should start monitoring all
packages if any rollback is available.
Handling the cases when a package without rollbacks fails and
mitigationCount equals 1.
Setting 'sys.attempting_reboot' property when we reboot after
committing the rollback, which would prevent factory reset to
execute synchronously.

Test: atest RollbackPackageHealthObserverTest
Bug: b/264997660
Change-Id: I12780acf8dcedb2b139d19339bc5acc632129ea0