Start rebootPromptAndWipeUserData from a separate thread in RescueParty

Call rebootPromptAndWipeUserData from currently thread in RescueParty
will cause a deadlock in PackageWatchdog when shutting down device, if the reset is triggerred by PackageWatchdog.
Forking a separate thread to execute it to release the lock.

Test: Trigger final level of rescue on a local device, and now can
successfully shutdown and boot into recovery mode.
Bug: 155780451

Change-Id: I3a901a469e172252deac9f6e4f1f2ab7a455fa58