Update PiPhi.py

Love the project but it took me a bit to get it to work just right. Decided to make the following changes after a bit of messing around.

* Added import subprocess
* Increased station list timeout to 2 minutes(Because I kept timing out and it was annoying)
* Added error handler for station list timeout with options to exit the program, reboot the Pi, or shut the Pi down.(Because it was annoying to time out and not know what had happened or have any options besides SSHing into the Pi)
* Added cleanExit call to Halt on Exit