Improvements to lock screen management:

- The window flag to hide the lock screen will now allow you to press home,
and automatically dismiss the lock screen if it is not needed for security.

- When opening the lid, if the lock screen will be shown, try to avoid
turning on the screen until it is ready.  There is actually still some
problem with this.

Change-Id: I51d769b8e6cff7b439b1ffea927c0a01376427b1