Usually you won't want to create a node in the root namespace,
and usually you won't want to use the Mininet API to set your
(real) default route, but if you do then you will probably want
to use a single command line to avoid disconnecting an SSH
session while we wait for the reulst of the 'ip route del default
command.

update examples README with new examples

Updating NAT class to use gateway interface

Also, passing CLI args to NAT constructor

fixes #437

use rcmd instead of quietRun when shutting down remote nodes

adding deleteIntfs option to switches and corresponding CLI command

use ControlPersist ssh option to fix ControlPath shutdown

fixes #448

Also adds docstrings.
Fixes #422