add ip per pod across vagrant minions

Vagrant+salt setup for providing a openvswitch based network for minions.
Pods will get an IP address that can be reached from across nodes/pods.

This PR is rebirth of #833 : 
https://github.com/GoogleCloudPlatform/kubernetes/pull/833

Improvements from before -
- The major issue was the flooding of the network with ARP loop packets. Because of that the network became unpredictable to TCP connections. That is now cured with spanning tree enabled on each docker bridge and openvswitch bridge.
- There is an end-to-end test that tests the vagrant setup  - 'sh cluster/vagrant/pod-ip-test.sh'. This will spin up a two minion cluster, install and run a server on both and check ping/curl from both hosts. The test destroys the cluster in the end. Improvements definitely needed in the test script (uses hardcoded pre-guessed IPs, does not check connectivity from within the container, cosmetic structure etc).
- The bridge-utils package will be installed whether the OS is Redhat or not.
- network_closure.sh script is in .gitignore


Can we use a smaller image?  

@brendanburns I had pushed a PR for a kubernetes/hello-kubernetes image, it would be good if we can get that built and available on the docker hub to use so we can pull a smaller image.  see https://github.com/GoogleCloudPlatform/kubernetes/tree/master/build/hello-kubernetes