martypy doesn't reconnect WiFi connection if USB cable is unplugged from Marty

[robdobsn]

To reproduce:

• Start using Marty with USB cable connected and using martypy to connect over WiFi
• Unplug the USB cable (which causes RIC to reboot)
• martypy gives no indication that the connection has been lost and does not attempt to reconnect it

Using MartySystemTests:

• use the Bug-Reconn-WiFi TestCase
• note that msgRxRateAvg initially is around 10 messages per second (martypy connected ok)
• note that it fails with msgRxRateAvg 0.0 after the reset