1129488 - Adjust Mongo Reconnect Support to Occur Indefinitely

https://bugzilla.redhat.com/show_bug.cgi?id=1129488

This fix adjusts the BZ behavior of Pulp<-->MongoDB reconnect support so that it will try to reconnect indefinitely. The previous behavior defaulted to trying 3 times, but allowed the user to override that amount with a config option. The config option is removed, and the retry support is adjusted to occur indefinitely in all cases.

There is also a change in scheduler.py because one portion did not have any reconnect support at all. With this PR, you can start all services, stop mongod for a long time, and then start mongod, and a sync will start with the first try.

This fix also includes doc updates to match.