[ActivityManager] Move top task to top in window manager

Symptom:
In certain situations, application starts activity while
it is in background. When an existing background activity
starts a new activity which results to be kept in the same
background task, the new activity won't be resumed.
In that case, the background task (sourceTask) should not be
moved to top in window manager.

Solution:
Move top task of the target stack to top in window manager

Change-Id: Id7a37ea67ce1f80e0c2b5399865c51fd7113deb8