Write log pusher PID to PID file.

The Jenkins log pusher daemon was not writing its PID to its PID file.
This prevented init from properly stopping the service. Write the PID
out to the file to fix this.

Change-Id: I35352b6e241b54a439f3675d02344d901249dff1
Reviewed-on: https://review.openstack.org/29578
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins