When unifying work profile challenge, keep the device lock
as long as it will still meet password requirement after unification.
If not, prompt the user to set a new device lock and only unify
work challenge after a compliant device lock is set.
Bug: 148630506
Fix: 149682344
Test: make RunSettingsRoboTests
ROBOTEST_FILTER='ChooseLockGenericTest|ChooseLockPasswordTest|ChooseLockPatternTest|LockUnificationPreferenceControllerTest'
Change-Id: I99cde2650902927f6a4cc7c0cc7c6016e0dc283f
f535e87e51