Config variables renames

More sensible variables names:

pri_a which is primary nameserver hostname, renamed to pri_hostname
sec_a which is secondary nameserver hostname, renamed to sec_hostname. 

pri_ptr is primary nameserver IPV4 address , renamed to pri_v4
sec_ptr is secondary nameserver IPV4 address , renamed to sec_v4
Following the scheme for IPv6 which is: pri_v6 and sec_v6.

Rename pri_net to server_net, prefix used for servers. (which generates an empty DHCP scope. (igor får ingen DHCP her nei) )