This is a regression in Nova when using XenServer 6.5, but it was also regressed by an upgrade to XenServer 7.0.
i.e. if you used XenServer 6.5 with Newton it worked, but if you upgrade hypervisor or you upgrade Nova then it no longer works due to 1) the change in network name (i.e. the XenServer 6.5 logic can't figure out what to do) and 2) the requirement to specify the network anyway.
This is a regression in Nova when using XenServer 6.5, but it was also regressed by an upgrade to XenServer 7.0.
i.e. if you used XenServer 6.5 with Newton it worked, but if you upgrade hypervisor or you upgrade Nova then it no longer works due to 1) the change in network name (i.e. the XenServer 6.5 logic can't figure out what to do) and 2) the requirement to specify the network anyway.