Automatic merge from submit-queue
Added option to specify the flannel backend, to cluster/ubuntu
```release-note
```
Generalized the cluster/ubuntu scripting so that there is a way to
specify the Flannel "backend" to use.
Also updated the default setting of ADMISSION_CONTROL, to match that
recommended for the latest release in
http://kubernetes.io/docs/admin/admission-controllers/#is-there-a-recommended-set-of-plug-ins-to-use,
and updated the comment on that setting to explain it.
Also made `cluster/ubuntu/reconfDocker.sh` sensitive to the `DEBUG` envar.
Deprecation Notice: This directory has entered maintainence mode and will not be accepting new providers. Please submit new automation deployments to kube-deploy. Deployments in this directory will continue to be maintained and supported at their current level of support.
The scripts and data in this directory automate creation and configuration of a Kubernetes cluster, including networking, DNS, nodes, and master components.
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