Fix race condition in Utilities::mvFileToFinalPath

Utilities::mvFileToFinalPath is used for moving files from "/_tmp.-ext to "/-ext" folder. Tasks write data to "_tmp" . Before writing to final destination, they are moved to "-ext" folder. As part of it, it has checks to ensure that run-away task outputs are not copied to "-ext" folder.

Currently, there is a race condition between computing the snapshot of files to be copied and the rename operation. Same issue persists in "insert into" case as well.