[Multi-user] Schedule full backup jobs immediately

All other schedule call sites for full backup and key value schedule
inline. The operation should be quick and scheduling on a separate
handler makes testing flaky.

Test: 1) atest RunBackupFrameworksServicesRoboTests
2) atest ScheduledBackupHostSideTest
3) atest ProfileScheduledJobHostSideTest
Change-Id: Id6ae557080da5a98c2ac572ca6b4b7973b7a9c29