use same directory for temp files as for log file

We keep `/tmp` on a separate file system. We wanted to move the segmentio log to `/var/tmp` because `/tmp` gets blown away on reboot.

So then `file_reader.py` starts throwing this error

```python
Traceback (most recent call last):
 File "/var/www/www.boat-ed.com/lib/Analytics/file_reader.py", line 133, in <module>
   os.rename(filename, processing_filename)
OSError: [Errno 18] Invalid cross-device link
```
Basically, can't mv files from `/var/tmp` to `/tmp` because they are different filesystems.