Proxy to retry on mongo Autoreconnect errors.

https://openedx.atlassian.net/browse/PLAT-71
I would tend to want to wrap only methods on collection. Wrapping cursor methods means that you'd be retrying a partially complete lookup, and I don't know if that's actually a sensible point to retry on a connection failure (the db you're reconnecting to might not have the in-progress query).