uptest.sh: Make more Mac-friendly

Thanks for this! I wasn't able to get the Python code to work on OS X 10.8 for some reason (every logged ping started with a 0, regardless of whether not I could ping out), and my Python's not so great, so I tried the shell script instead. I had to make two tiny tweaks to be able to use the uptest.sh output with upmonitor.py. Maybe they're useful to you too...

- Create ~/.nbsstate if it doesn't already exist
- Change log format to match that of upmonitor.py