As part of the move to make all HAL operations a ClientMonitor,
this change makes generateChallenge return the challenge via a
callback.
Added generateChallengeBlocking() so that existing synchronous clients
can continue to work with minimal changes (only renaming is necessary),
and so that it's explicit that the call may take some time (up to
hundreds of milliseconds on some devices).
1) LockSettingsService#resetLockout path
2) Fingerprint/Face enroll path
Bug: 157790417
Test: Enroll on fingerprint/face devices
Test: ResetLockout on fingerprint/face devices
Change-Id: I99efc1c72c8ac994c56d6d2deaf3e0131e5b2dac
706e17d7dc