update CoreOS installation guides

* CoreOS guides now use the 0.5.4 official release binaries
* kube-register has been updated to work with the 0.5.4 release
* flannel uses the vxlan backend by default for better performance
* cloud-configs are used for all examples
* instructions for GCE, AWS, and VMware Fusion have been combined
Nit -- might be worthwhile to call out that this uses flannel for networking too.  That is one of the main reasons that the same set of instructions can be used easily across different clouds.  When moving to a production deployment, users probably want to investigate the ideal networking setup for their environment.