Cause: with unified screenlock, ConfirmDeviceCredentialActivity didn't
forward result with FLAG_ACTIVITY_FORWARD_RESULT
Also, fixed that ConfirmDeviceCredentialActivity didn't allow fingerprint
authenication in unified screenlock after keystore unlocked.
In ChooseLockSettingsHelper, add one new util function to allow
extra option to set returnCredentials to false while external to true.
Set StrongAuth to "not required" when it has been successfully unlocked.
Test:
1. PO Unified Screenlock/Work Challenge x fingerprint -> ok to trust cert
(Also, no credential is returned in intent)
2. WorkMode off -> Reboot -> turn on Work mode
-> no fingerprint option, PIN unlock successful to turn work mode on
Bug: 28752364
Change-Id: I6dc8865e8f005545f8577d7731afb4495647062b
5e0a46bff6