Network may now be used with custom controllers.
An example of doing this is in nox.py, which instantiates at TreeNet
using a custom Controller, NoxController, that runs nox_core rather
than the reference controller.

This should eliminate ofprotocol bogons living on past the end of a test.

Added scratchnetuser.

low-level primitives.

The "nox.py" example attempts to use nox as a controller rather than
controller(8).

More edits for INSTALL and README, and refinements for sshd and xterm
examples.

Fixed xterm.py (and cleanup) to clean up screen sessions.
Cleaned up sshd.py (though interface is still in flux.)
Added 1024-node network example (treenet1024.py).
Added example showing multiple tests on a single network (multitest.py).
Renamed examples to make them easier to type!

Other minor cleanup.

Minor tweaks to other files.

More edits for INSTALL and README files.
Batteries still not included (for the moment.) ;-)

the node is running in the root namespace.

More tweaks for examples, which are still in progress.

(It also adds a route from the root namespace to the data network via
the first OpenFlow switch, so when you ssh in you go through OpenFlow!)

Modified Network() to optionally decouple starting the network, running
tests, and stopping the network. This allows multiple tests to be run
(or additional modifications to be made to the network before actually
starting the switches and controller.)

Still tweaking xterms - it sort of works but the screen sessions are not
cleaned up, which leads to nasty garbage.

Added new example to create xterms.
Other minor changes.

Modified cleanup to use dpctl to remove kernel datapaths.

Ping and iperf tests now return something possibly useful.

Node -> { Host, Switch, Controller }
Network -> { TreeNet, GridNet -> LinearNet }

Modified cleanup to clean up kernel datapaths.