improvements to VPNLabelledPrefix
improvements to VPNLabelledPrefix

* internal rd and mpls fields are RouteDistinguisher and Labels objects
* more useful repr

blablacar/exabgp,benagricola/exabgp,dneiter/exabgp,benagricola/exabgp,benagricola/exabgp,earies/exabgp,dneiter/exabgp,earies/exabgp,blablacar/exabgp,earies/exabgp,blablacar/exabgp,dneiter/exabgp