ClientMonitor should only send cancel() once to fp daemon

This is already done for AuthenticationClient.

This should be done for all ClientMonitor subclasses which override
stop(), otherwise hardware and framework will be in inconsistent states.

Fixes: 38463417

Test: 1) Open fp settings in background, enter keyguard, dismiss
keyguard with fp and make sure settings can "authenticate"/highlight
fp when touched

2) Enroll fp and go back/forth between FingerprintEnrollFindSensor
and FingerprintEnrollEnrolling. Make sure touching fp sensor
will always bring you to FingerprintEnrollEnrolling

Change-Id: Iee3d03c8a8b3445073740fbfbe411f12172afe23