5.3 user root persistence migration can indadvertantly delete user roots

[mudinthewater]

Describe the defect

Despite receiving an http:200 on the /user//root object for 6 users, 5.3 initiated new object PUT requests overwriting the user persistence storage.

Expected behavior

Not do that

Steps To Reproduce
Is network related! This can be reproduced or simulated by loading OMM, then disconnecting from your network and interacting with user folders. OMM will request a new root be created if you interact with the user folder.

This can cause issues with spotty network connections, where one connection may fail but another succeed - i.e. if download was briefly interrupted but upload wasn't, OMM could wipe the entire user folder list, which is what we've seen in logs.

Additional context

crit4 - Now that we know the cause I've coded FastMIO to 409 conflict on these create requests if they already exist. This should provide plenty of time for the bug to be addressed in the next release cycle. Should verify that MCWS also 409 conflicts, otherwise this could be a 2.