xenapi - use management network to reach OS VM

Devstack used the HOST_IP_IFACE to reach the OpenStack VM through ssh.
This patch changes this behavior, so that the IP address of the
interface connected to the management network will be used.

Related to blueprint xenapi-devstack-cleanup

Change-Id: I7f34d973870792d60a33ea512901d9b0d422150b
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

Conflicts:

	tools/xen/functions