test: add network template tests

tests/network/templates/preseed.pkrtpl

@@ -0,0 +1,9 @@
+d-i netcfg/choose_interface select ${device}
+%{ if ip != null ~}
+d-i netcfg/disable_autoconfig boolean true
+d-i netcfg/get_ipaddress string ${ip}
+d-i netcfg/get_netmask string ${cidrnetmask("${ip}/${netmask}")}
+d-i netcfg/get_gateway string ${gateway}
+d-i netcfg/get_nameservers string ${join(" ", dns)}
+d-i netcfg/confirm_static boolean true
+%{ endif ~}