Comment 14 for bug 1684993

Reviewed: https://review.opencontrail.org/30655
Committed: http://github.com/Juniper/contrail-controller/commit/52f203ea478e4f6721b3b0016211d48b531e4c57
Submitter: Zuul (<email address hidden>)
Branch: R2.21.x

commit 52f203ea478e4f6721b3b0016211d48b531e4c57
Author: Praveen K V <email address hidden>
Date: Fri Apr 21 15:21:31 2017 +0530

Replace tbb::task::spawn() by tbb::task::enqueue() and also support for task monitoring

Replace tbb::task::spawn() by tbb::task::enqueue(). enqueue() is more
appropriate call since task library just fires the task without calling
spawn_root_and_wait()

Also, introduced a TaskMonitor class which monitors number of tasks
enqueued to scheduler and number of tasks spawned by TBB. If the monitor
finds tasks are enqueued but not scheduled for a configured time, it
will exit the program.

Change-Id: I0db61f60c8fef5c66c6deff6b58516b293628585
Fixes-Bug: #1684993