Made AWS region and ami to be configurable through the ENV variables.
Added install instructions for RackSpace cloud using Ubuntu 12.04, 12.10, 13.04
updated the rackspace docs to have more information, and fixed a couple of mistakes
fixed the git clone url, it was the read-write one that required ssh access to the docker account, changed to the read only version
Make sure that the layer exists prior to store it
Merge pull request #597 from dotcloud/589-volumes_crash-fix

- Runtime: Make sure that the layer exists prior to store it
Merge pull request #588 from kencochrane/rackspace-docs

+ Documentation: Added install instructions for RackSpace cloud using Ubuntu 12.04, 12.10, 13.04 and fixed a few minor issues with the ubuntu install docs.
Merge pull request #586 from tbikeev/master

* Vagrant: AWS region and ami name can now be set as ENV variables.
build docker using Go 1.1
Merge pull request #598 from unclejack/build-docker-with-go1.1

* Dockerbuilder - build docker using Go 1.1