[FLOC-984] Document rackspace deployment

Rackspace seems to be the easiest deployment of all. 

Their Fedora 20 image has a sufficiently new kernel (3.16.4-200.fc20.x86_64) to run ZFS, so all that's required is to install the devel package from koji...but that's in the general Fedora 20 installation instructions.

Built atop #974, so merge that before reviewing this.

Fixes https://clusterhq.atlassian.net/browse/FLOC-984
I think 8GB seems a bit OTT, but yes they should be consistent and the AWS instructions specify m3.large which also has ~8GB RAM. I'll change it.