Description:
This change alters the way that read preference is handled in mongos. Specifically, it is the commit which implements PM-856
Engineering Ticket Description:
Inside the ARS, support use of the TaskExecutor::scheduleRemoteCommandOnAny method, which will allow the ARS to use any acceptable host returned from targeting, rather than requiring us to use one at random.
This should allow us to prefer routing requests to hosts which have ready connections to, or that we can generate ready connections to faster