(2.12) Refactor NIC configuration for Xen
(2.12) Refactor NIC configuration for Xen

Extract common code between the PVM and HVM Xen hypervisors regarding
NIC configuration.

Signed-off-by: Jose A. Lopes <0fb9c4f8511df4ec2ae28af879e9d462f6218a2c@google.com>
Reviewed-by: Hrvoje Ribicic <be5828fca31f89218048bec4189e30a581aa65da@google.com>

apyrgio/snf-ganeti,apyrgio/snf-ganeti