Bugreport Manager service clear binder identity

Binder identity of the caller needs to be cleared before making a call
to ensureIsPrimaryUser() and is later restored for the rest of the code
to execute.

Test: Manually by triggering bugreports from 'settings' using bugreport
API.
Change-Id: Ida781b633efbea57a9442fb9a8a5f823f9acbe8b