Add cluster setup documentation for OpenStack.

The EC2 documentation makes it very easy for new users to spin up CoreOS
clusters, but the OpenStack docs focused on single instances. I modified the
OpenStack docs to help walk new users through creating a cluster. Portions were
copied (adding more machines & multiple clusters), and slightly modified to use
OpenStack terminology.

I also split long `nova` & `glance` commands across multiple lines to help with
readability and modification.
Merge pull request #118 from robszumski/master

feat(getting-started-docker): rewrite commiting a container instructions
Removed duplicated "the" word
Merge pull request #119 from waldman/patch-1

Removed duplicated "the" word
feat(quickstart): link to guide for turning off auto reboots
etcdctl delete was changed to etcdctl rm, reflecting this in the docs
Merge pull request #120 from Niessy/delete-deprecated

etcdctl delete was changed to etcdctl rm, reflecting this in the docs
Merge pull request #117 from amerine/openstack-cluster

Add cluster setup documentation for OpenStack.
fix(getting-started-docker): fix broken link to docker CLI
feat(journal): add fleetctl instructions for reading the journal