Not removing primary TaskFragment when clear task

Placeholder activity was finished while starting the
task root activity from launcher because the task
root activity was set as singleTask launch mode.
Meanwhile, the primary TaskFragment was also removed
because of the split-rule finishPrimaryWithSecondary.

Sending the information of whether the last activity
on the TaskFragment was finished due to launch other
activity to client. So that the organizer can decide
whether the primary TaskFragment should removed.

Bug: 196179714
Test: relaunch singleTask activity with placeholder

Change-Id: I9a0369285adfbdef1edc5a7f2af944ec5b434566