Use unique folders to remove chance of name collisions

Summary: Make sure we a unique temporary folder for operations that could be called concurently (which is most of our APIs) to avoid local file path collisions.

Reviewed By: kiminoue7

Differential Revision: D50102331

fbshipit-source-id: 313648cb73ee3b9a0403beb1634e9fa01508916f

vrs/utils/FilteredFileReader.cpp

@@ -212,7 +212,7 @@ int FilteredFileReader::openFile(unique_ptr<FileHandler>& file) const {
 string FilteredFileReader::getCopyPath() {
   // if uploading, but no temp file path has been provided, automatically generate one
   string fileName = getFileName();
-  return os::getTempFolder() + (fileName.empty() ? "file.tmp" : fileName);
+  return os::makeUniqueFolder() + (fileName.empty() ? "file.tmp" : fileName);
 }
 
 bool FilteredFileReader::afterConstraint(const string& after) {