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


The smallest image should be nice for the current test. 
Though in future some more detailed test steps may want a ssh/bash to be possible to the container itself. Especially when we want to really know what network addresses got assigned to the container and not just guess based on docker's way of counting things.