Address PLFM-2179 by inserting 'rolling' to the files that are still being rolled over so that the files without the 'rolling' name can be picked up by dashboard for metrics.
Now also rolls over the batch even if the batch has only one file.
Extend the merge worker's interval to 1 hour.
Merge pull request #826 from eric-wu/develop

Address PLFM-2179 by inserting 'rolling' to the files that are still rolling