nuageinit: add support for OpenStack network config

Add naive support for openstack network config.
if no config driver have been found, try to detect that we are running a
VM on openstack via the smbios information, use the first iface
available and temporary activate dhcp on it, to be able to fetch the
necessary informations for cloudinit.

While here make the rc script execute after devmatch, some ethernet
device might be attached via devmatch and may be needed for cloudinit.

Tested on OVHCloud Public Cloud.

MFC after: 3 weeks
Sponsored by: OVHCloud