Changes to support Contrail VRouter as a forwarding data path option
in Xen (similar to OpenVswitch).

The changes include
* Adding a new network option to the /etc/xensource/network.conf file
  (contrailvrouter)
* Changes to xcp-networkd, xapi daemon to support contrailvrouter
* Module to handle calls to the Contrail Vrouter from XAPI
* Changes to vif script to handle calls if the network option is
  contrailvrouter
* The control component of Contrail VRouter (contrail-vrouter-ctl)
  is not part of the change and will be installed as part of the
  Contrail Vrouter RPM for XenServer.
* Changes also include to add ContrailVRouter as an option in the
  netman library.