Small networking related optimizations in mongos:

1. We parse the command result from each response but only inspect it if the request was a hedged read.
2. The readReplyMetadata hook takes a StringData replySource, which requires the NetworkInterfaceTL to use toString() on a HostAndPort, but seemingly nothing uses replySource
3. It looks like we copy a boost::optional<shared_ptr> on each call to AsyncDBClient::runCommand() when we can std::move it