Ubuntu apt source location was wrong; Don't block logrotate if server is not running.

Two fixes.

* Ubuntu apt source location issue. See http://docs.mongodb.org/manual/tutorial/install-mongodb-on-ubuntu/
* Logrotate should not be blocked when mongod or mongos is not running. It's common (for me) to run mongod without mongos (on db server) or mongos without mongod (on front end server).