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
Merge "xenapi - use management network to reach OS VM"