Check for keyguard occlusion on camera lift

Instead of just checking if the keyguard is locked, check that it's showing and
not occluded. Also add more logging.

Bug: 62386862
Test: Attempted lift gesture from the following states:
1. Locked
2. Suspended
3. Incoming phone call while locked
4. In phone call while locked
Change-Id: I55e75c695c9f1349ca16791a25029bf33477d7b7