Fixed AutoYast Import() and Write()

- bnc#898659
- Imported zones were not written to the system as they were not marked as 'modified'
- Directory /etc/named.d/ was used even if it didn't exist
- The whole named.conf was rewritten from scratch as Yast thought that something has changed that file while Yast was running
Regarding the need to modify the iterated array: it contains references to hashes, so this should just work™.
```perl
for my $z (@zones) {
  $z->{"modified"} = 1;
  y2milestone("Imported zone: ".$z->{"zone"});
}
```