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.

Approved by: re (cperviva)
MFC after: 3 weeks
Sponsored by: OVHCloud

(cherry picked from commit 2775b9b0bcc278dd4183b57784953c26a3fcdc89)
(cherry picked from commit 6c682f5c3860a49cd0440599fffe1106c00ff830)