[SettingsProvider] fix WriteFallbackSettingsFilesJobService holding wakelock

onStartJob() should return false otherwise the job service will hold a long wakelock until it times out. writeFallBackSettingsFiles() is blocking, so when it returns we should finish the job.

BUG: 162438758
Test: manual
Change-Id: I3bfbcf5a7b21f142fd00130e1a57232bc02aedb6
(cherry picked from commit 69088854)
Merged-In: I3bfbcf5a7b21f142fd00130e1a57232bc02aedb6