Blocker Description
Secondary name-node fails in the middle. The main name-node writes its journal transactions into edits.new at that time.
If the name-node is shut down after that and restarted, then loadFSImage() reads current image file, merges it with the edits
file and with the edits.new file.
Now saveFSImage() saves new image file, creates empty edits file, and then calls rollFSImage(), which particularly renames
edits.new into edits. This is a mistake, during startup edits.new should be merely removed after merging it with the image.
The purpose of calling rollFSImage() during startups imho is to recover from an unsuccessful checkpoint. So an easy fix
is to empty edits.new before calling rollFSImage the same as edits are emptied, then rollFSImage will rename empty file
to empty which gives us the desired result.
We should fix this bug both in 0.14 and 0.15. I make it a blocker for 0.15.