SERVER-39835 creates logic to run a delete-insert transaction from mongos upon receiving WouldChangeOwningShard. If the original write command is not part of a multi-stmt transaction, instead of creating and running delete and insert command objects we will instead start a transaction and run the original write command. This command should use the original query predicate and updates attached to the WCOS as its query and update fields. Once this returns successfully, commit this transaction.