fixes #8314 - static network config for preseed

- fix ignored static network info when pxe booting
  o see debian manual https://www.debian.org/releases/wheezy/i386/apbs04.html.en#preseed-network
- pass static var to finish template
  o if network config is static then host+domain need fixing in finish template
- update host/domain name if using static network
  o when pxe booting via dhcp, debian ignores get_hostname & get_domain string within d-i