Bring up unlock screen for FLAG_DISMISS_KEYGUARD.

Widgets that did not launch Activitys would not display the unlock
screens when they were tapped. Now any window that is shown with
FLAG_DISMISS_KEYGUARD set while the keyguard is locked will
cause the unlock screen to be displayed.

Bug: 7301530 fixed.
Change-Id: I90d11b52d2b63260bdb5f2b6eb7e98eb7a4d9331