Vivid is EOL, and Docker is no longer packaged for it.
Remove support for it in 1.3 (in 1.2 we had warned users it was EOL).
Also remove unused wheezy, trusty & coreos & do general cleanup.
Default distro is jessie, due to the support situation with Ubuntu
distros. Default ubuntu distro is wily.
Update the docs to reflect the recommended distros with kube-up, and to
encourage contributions for other distros.
For parity with GCE, we really want to support aufs.
But we previously supported btrfs, so we want to expose that.
Most of the work here is required for aufs, and we let advanced users choose
devicemapper/btrfs if they have a setup that works for those configurations.
We were specifying a region, but naming it as a zone in util.sh
The zone matters just as much as the region, e.g. for EBS volumes.
We also change the config to require a Zone, not a Region.
But we fallback to get the information from the metadata service.