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

    This argument expect a parameter which is the version number of OVS you wish to install.
    install.sh -V 2.0.0

    What is nice that I tested, is that you can keep running the above to change
    which OVS version you want to test with.  Also, if a new version of OVS
    is released, just run the above again specifying the new version number.

    The version number must match the version number in the tarball file name
    like openvswitch-2.0.0.tar.gz.  In this case, the version specified
    must be 2.0.0.

This is added because we install Ubuntu from a serial console.
Fixes #265

should facilitate importing 64-bit image

fixes #261

fixes #212