StatusBarWindow: Fix collapse using Back button

Implements the missing dispatchWindowFocusChanged method to allow the StatusBarWindow (Notification/QuickSettings) to collapse when the user presses the back hardware key.

Change-Id: Id77955d6286d83ddf5e0e05779446c2e978ff4de
fb: remove KeyguardTestActivity

absolutly not needed only for test cases we can revert it locally if needed

Change-Id: Ifef814f20533fc0ed51eb1988733ad365b2e52fa

Conflicts:
	packages/Keyguard/test/res/drawable-hdpi/app_icon.png
	packages/Keyguard/test/res/drawable-mdpi/app_icon.png
	packages/Keyguard/test/res/drawable-xhdpi/app_icon.png