Set correct Nova NIC boot option

Update Nova NIC boot options to reflect the CLI Nova option names.
That patch keep precedent attribute name to preserve compatibility
with old template.

Signed-off-by: Édouard Thuleau <edouard.thuleau@cloudwatt.com>
Change-Id: I9b4a939a2ced4e9157df8685052cbe7594061ac8