get-my-ip.py: Add a script for getting your public IP address

This will help students connect to each other on the LAN during class.
Note that if you ping a host across a NAT, you'll get your IP inside
the NAT, not the NAT's IP.
get-my-ip.py: Python 2.x sockets can't be used in 'with' statements

They don't have __exit__.  Use an explicit try/except block to be
compatible with both 2.x and 3.x.
Merge remote-tracking branch 'wking/get-my-ip'

Adds a small Python script for getting your IP address on the local network.