FIX: Set INSTANCE_NICn_NETWORK_NAME only if net is defined
FIX: Set INSTANCE_NICn_NETWORK_NAME only if net is defined

Found by pylint's using-constant-test warning. 'network' is a module,
'net' is the network name for this NIC.

Signed-off-by: Brian Foley <a00e555871a6a538e97f8c44307104c884f8e869@google.com>
Reviewed-by: Viktor Bachraty <a13ea37fcfcda126dc54f94389ded93f402eee93@google.com>

yiannist/ganeti,mbakke/ganeti,mbakke/ganeti,ganeti/ganeti,onponomarev/ganeti,yiannist/ganeti,ganeti/ganeti,andir/ganeti,mbakke/ganeti,yiannist/ganeti,ganeti/ganeti,andir/ganeti,andir/ganeti,onponomarev/ganeti