SERVER-9253 `rpm/init.d-mongod stop` unnecessarily sleeps for 5mn

`/etc/init.d/mongod stop` uses killproc with a 5mn delay between TERM and KILL.
In most cases this 5mn sleep is too long and the stop command hangs unnecessarily even though the process has exited successfully.

This ticket is to re-implement the same 5mn delay but with a busy-wait loop that would return as early as possible.

https://jira.mongodb.org/browse/SERVER-9253
When I ran this script on a test machine, the process sometimes did not go terminate before the first check of the loop condition, resulting in the script unnecessarily sleeping for 10 seconds. Perhaps we can add a tiny delay here before entering the while loop.