Skip test_cpu.py if RT_GROUP_SCHED is not enabled

use udp with iperf to measure loss. pings are not reliable

measure loss with udp iperf

This should more reliably shut down pexpect subprocesses when
build.py exits before completion.

Switch to loxigen-built openflow.lua wireshark plugin

Apparently there is a conflict where the lua plugin
conflicts with the built-in dissector for openflow
that is included with 1.12 and up. For now, we will
just not install the plugin. This should fix the
14.10 VM build.

Additionally, I have added a handy function,
version_ge, which compares version numbers in
canonical x.y.z format. Thanks to stackoverflow for
pointing out the incredibly useful sort -V option!

The older wireshark dissectors were not well-maintained
and were a pain to build. They also added tons of extra junk
into our VM images! The ones built into the current
wireshark are deficient for 1.3. The solution for the
future is almost certainly to go with the lua-based plugin,
since it is architecture-independent and should be much
easier to maintain and upgrade.

A simple mobility API and example

fix host --rt 

adding 'ports' command to cli

adding example and test for intf.config()

parse comments out of CLI

check if RT_GROUP_SCHED is enabled in kernel

if we do not receive a ping and cannot parse output, return errorTuple

Cluster Support Prototype

Fix runCpuLimitTest with multiple cores

We add a new experimental feature to allow Mininet to run across
a cluster of machines. This is currently implemented via a set
mix-in classes that provide remote nodes that are implemented
via a connection to a remote shell, and remote links which are
tunnels across servers. In this preliminary implementation,
both control and data connections are made via ssh, but this
could change in the future.

A MininetCluster class is provided which allows existing code
to be used with minimal modification - all that is required is
to provide a list of servers to use. A customizable placement
algorithm may also be specified. An experimental CLI subclass
is also provided to make it easier to examine node placement;
status and links commands can also check whether nodes and
tunnels are still running.

Although this is an experimental feature, it does include a
--cluster option to make it convenient to start up a Mininet
simulation over a cluster, and a script to assist with setting
up the prerequisite authentication via ssh key pairs.

The cluster feature is preliminary and missing some obvious
important features, such as parallel startup and multiple tunnel
types, which we hope to add in the future.

file no longer returns image size on 14.04
fixes #373

Fixes #372

Since chroot() doesn't chdir() by default, we are left in
an unreachable directory in node.pexec() (and in xterms.)

fixes #370

Fix output of backgrounded processes

print useful output for tests upon failure