Adds JUJU to the Kubernetes Provider listing

This feature adds Juju provisioning to the kube-up script. It currently
parses out the pre-requisits on debian/ubuntu based systems and installs
them if they are missing.

From there we followed the integration path that was found in the
libvirt-coreos path, implementing the methods found in the boilerplate
and calling juju service calls. There are a few "arbitrary sleeps" in
the code to allow the cloud provider to settle and properly deploy.
These are work-around cases from the script executing faster than juju
was able to communicate from the state server to subsequent nodes. I
left comments inline at these points.

To exercise this:

    export KUBERNETES_PROVIDER=juju
    cluster/kube-up.sh

It will spin up a ref arch with 1 Kubernetes Master, 2 minions, and run
the cluster validation checks against the deployment. Bridging the gap
between the juju specific bits and the upstream recommended guides for
getting started with Juju.

To note, if you do not have a "current environment" set in Juju, it will
spin up the quickstart integration wizard in interactive mode, allowing
you to configure juju, and add the proper provider/use it. Otherwise it
assumes you're in the provider you wish to use, and will deploy there.

cluster/kube-env.sh

@@ -18,7 +18,7 @@
 # You can override the default provider by exporting the KUBERNETES_PROVIDER
 # variable in your bashrc
 #
-# The valid values: 'gce', 'gke', 'aws', 'azure', 'vagrant', 'vsphere', 'libvirt-coreos'
+# The valid values: 'gce', 'gke', 'aws', 'azure', 'vagrant', 'vsphere', 'libvirt-coreos', 'juju'
 
 KUBERNETES_PROVIDER=${KUBERNETES_PROVIDER:-gce}