Remove the flocker-node installation instructions - fixes 457

We've decided to remove the `flocker-node` installation instructions for now. 

They can be re-instated when we've sorted out our RPM build and distribution process and when we better understand the various SElinux problems that seem so common. (eg https://github.com/ClusterHQ/flocker/pull/532#issuecomment-51805815)

Fixes #457