Fixing issue with empty Recents screen.

- We did not expect RecentsActivity to be launched without going through
  the normal SystemUI controls, but when the home activity is in the foreground
  and killed (via a normal apk update), the RecentsActivity stores the old
  launch configuration and believes that it was launched from home and awaits
  the animation-complete callback to animate the tasks in.
- This CL adds a workaround where the configuration is reset whenever
  RecentsActivity is stopped, which allows the tasks to be shown immediately
  if the User is kicked back into Recents due to an update.

Bug: 22542869
Change-Id: I2b4168ccecfbf868fa6d544fe89109dfa74f51df