xenapi - cleanup network configuration

The Xenserver/XCP part of devstack was configuring the hypervisor's
connectivity to the outer world, by adding VLANs, and physical
interfaces to the virtual networks. It added a lot of complexity, and
made it hard to get started with XenServer. This patch removes that
extra complexity, so it is left as an exercise for the user.

Related to blueprint blueprint xenapi-devstack-cleanup

Change-Id: If3367335c3da8621d0afe1f6cae77511fbdbb3e2
Merge "xenapi - cleanup network configuration"