Fix disappearing biometric prompt for the managed profile

In several circumstances, the ConfirmDeviceCredentialActivity
may be started while the device is being unlocked - particularly, when
the managed profile on the device has a separate challenge and the user
is attempting to start an activity associated with the locked, managed
profile. For example, by double-tapping a notification from the managed
profile or trying to reply to such a notification.

When the ConfirmDeviceCredentialActivity is started after the user has
entered the primary lockscreen challenge but before the keyguard is
fully dismissed, the activity may be started and immediately paused.
If the activity then calls finish() in onPause(), the biometric prompt
will disappear and the user will not have a chance to authenticate.

Fix the issue by only calling finish() in onPause() if the biometric
prompt has not been shown.

The flag indicating whether the activity is waiting for biometric
prompt or not needs to be cleared whenever the biometric prompt invokes
the callback, so that the activity will correctly call finish() if the
user does abort authentication.

Bug: 153689182
Bug: 141470517
Test: Manual, set up a work profile and double-tap a work notification
or try to Reply to a work GMail notification.

Change-Id: I9d3d3000b99d0eb4b44b90f5a0c2856db5f32144