Revert "Changes to support Contrail VRouter as a forwarding data path option"

This reverts commit 7f58e91ece221b2737f6c46aa189a503a529d1a3.
Changes to enable contrailvrouter as a networking option in
XenServer.

* Changes to xcp-networkd and xapi daemons to accept
  contrailvrouter as a networking option in the
  /etc/xensource/network.conf file
* New module ContrailVR to handle commands that are
  received from XAPI daemon and pass it on to the
  corresponding Contrail Vrouter control module.
* Changes to script to change network backend.
* Changes in VIF script to handle contrailvrouter
  to add, remove, online, offline VIFs