Retried findAndModify requests can slow log/profile into the wrong namespace

A variety of callers can use AutoStatsTracker who's constructor changes the namespace state of an operation.

However, the destructor does not restore the state. Thus a retried findAndModify can log a slow query/system.profile entry under the config.image_collection namespace.

While this is probably a subtle yet widespread problem, this ticket aims to correct the scenario just for the config.image_collection lookup in the findAndModify code paths.