(SERVER-150) flush jruby instances

I have a slight preference for @KevinCorcoran's patch solution but that is based on no further arguments needing to be passed around.  Suppose we could also create a single composite argument, maybe just a map?, that could be updated later without having to add parameters in multiple places.  In the interest of getting the work for this in sooner, though, I'd propose we just preserve what's currently on the PR for now and defer the other work out to a different ticket for later.