Use FQDN as PTR name instead of octet

Alternate version of slapers pull request.

This patch need when we have multiple PTR zones. In a current state next code will create an exception:
dns::record::a {
 'dns1': zone => 'test', data => '192.168.10.1', ptr => true;
 'dns2': zone => 'test', data => '192.168.11.1', ptr => true;
}