MultiprocessWSGITest wait for workers to die bug

MultiprocessWSGITest.test_terminate_sigterm
fails because the wait for workers to die is unreliable.

Parent process can now wait on child or grand-child
processes to complete before moving on. This allows
for grand-child (aka worker) processes to take as much
time as they need to shutdown. NOTE: If the processes
still take too long, they will be killed by the test
framework throwing the "TIMEOUT" exception.

Reverts to using a ping signal to child process
to determine if the child process is live. Waits for
the signal call to fail, signaling process death.

closes bug #1218133

Change-Id: I08e17005508fe412f462773f9ab212cf0f10382f
Merge "MultiprocessWSGITest wait for workers to die bug"