Now you can type commands into each mini-console!

The console tool spawns and monitors a bunch of nodes.

Moved monitor() and readline() into net.py and node.py respectively,
which will hopefully be useful for monitoring large sets of hosts,
as is done in udpbwtest.py.

Changed iperf to use interactive command infrastructure (such as it
is), which may make it more reliable. Hopefully it's a bit clearer
as well, although it is slightly more complicated.