For getHomeActivity() only return current user.

Previously getHomeActivity() returned the topmost home activity
independent of which user was currently running. That defeated the
purpose of the method. This fix returns the home activity of the
current user or null if one has not yet been created.

Also remove some cruft that accumulated.

Fixes bug 21055376.

Change-Id: Ic1d58129aedbe3624f8a9d12c05c84674687b0a4
diff --git a/services/core/java/com/android/server/am/ActivityStackSupervisor.java b/services/core/java/com/android/server/am/ActivityStackSupervisor.java
index 5eee34f..39df9d1 100644
--- a/services/core/java/com/android/server/am/ActivityStackSupervisor.java
+++ b/services/core/java/com/android/server/am/ActivityStackSupervisor.java
@@ -2658,7 +2658,7 @@
     }
 
     ActivityRecord getHomeActivity() {
-        return getHomeActivityForUser(UserHandle.USER_ALL);
+        return getHomeActivityForUser(mCurrentUser);
     }
 
     ActivityRecord getHomeActivityForUser(int userId) {