[WiFi part 3] network connection recovery

[bplimley]

I've observed on my desk at LBL that occasionally the pi will lose the wifi connection, even though lbnl-visitor is still good.

A simple solution is to restart the network connection using:

sudo ifdown wlan1
sudo ifup wlan1

These can be run from NetworkStatus with a subprocess.call or .check_output (link).

But there should also be some checking on whether the pi is actually using wifi, e.g. do a quick check on /etc/network/interfaces.

[bplimley]

See issue #52. This may recover the network but it might also crash the subprocesses.