Ensure Ryu-RFProxy is installed from vandervecken

Previously we fetched from the 'master' branch of the routeflow
repository on github. This changes it to follow vandervecken.

Signed-off-by: Joe Stringer <joe@wand.net.nz>
Install newer Ryu versions

Signed-off-by: Joe Stringer <joe@wand.net.nz>