[ActivityManager] Avoid keeping restarting home when only home activity exists.

Root Cause:
When there is only home activity existed,
updating home apk will call forceStopPackageLocked to finish the activity.
Then activity history becomes empty, then home will be launched,
but its package is still target to close that results a loop.

Solution:
If home activity has been force-stopped, do not stop the same home activity again.

Change-Id: Icff12028d407873c2e6f50a06bcad231b908ccbd