Ensure files are deleted when we're done with them [MJ-940]

I went ahead and linked /tmp/parse_log to /mnt/tmp so we have a bit more space if something bad happens again. In the event that that link gets deleted, this will create a subdirectory in /tmp so we don't pollute it like munin does.

Permissions should be okay - celeryd is started by root, /mnt is owned by user ubuntu, /mnt/tmp is owned by root.

All tests pass.