Rackspace - Switch to CoreOS for standard cluster

The Rackspace setup for Kubernetes now leverages CoreOS instead of Ubuntu. We've dropped Salt completely for our cluster.
Add Rackspace to build/release.sh

Updates to the build/release.sh scripts to upload build binaries to
Cloud Files.
remove hardcoded cloudfiles path and fix PORTAL_NET
Migrate Rackspace upload scripts to util.sh

The functions to upload built k8s tars to Cloud Files were incorrectly
placed in build/common.sh. These have been migrated to
cluster/rackspace/util.sh
Remove extra newline and update comments in util.sh
Merge pull request #1832 from doublerr/rackspace_switch_to_coreos

Rackspace - Switch to CoreOS for standard cluster