Propagate launch root task for consecutive launch

Propagate launch root task for consecutive launch to ensure trampoline
activities will be launched into the same root task. And prevent the
indicated target-root-task been overrided with the root of reusable
task.

Fix: 193095759
Test: manul check trampoline activities will be launched into indicated
root task.
Test: atest ActivityMetricsLaunchObserverTests# \
testConsecutiveLaunchNewTask

Change-Id: Ic75c7efbf120562fc284c6ee12d49d2f736a42ec