Call netns using setsid to detach from the tty; this is
intended to fix the problem of control-C killing your network.

sendInt() doesn't actually work - hopefully we can fix this in the
future, but it's tricky since we want to detach the many shells from
our tty, but then optionally send tty interrupts to them! Ideally we
would either know the pid of the subprocess or be able to send a signal
to bash to get it to interrupt its subprocess.

waitOutput() now uses monitor. We also handle sentinels
coming in the middle of output (but default at end should
still work well.)

We need to figure out how to specify the IP addresses for the
routed control network. For now I'm going back to 192.168.12x.y

Also changed controller params to use IP strings rather than
numbers. However, we still need to clarify what ControllerParams
is actually for.

Still could be better though.... and we need more topology
examples.

Later we may wish to optimize this so that the arg lists are
not created if the logging level is too low.

Also changed the str format for nodes to use str() rather
than repr() so we don't end up with extraneous quotes.

Also tweaked cmd/cmdPrint to make them more beautiful and functional,
and a few other minor changes, such as using a new idiom for verbose.

These changes support reinstating the examples.