Add record definition in dns::zone define

With this PR one can define it's RRs in its definition of the
dns::zone. RRs Supported: NS, MX, A, AAAA, CNAME

It does allow zone definitions as follow 

    dns::zone {'example.com' :
        soa => 'ns1.example.com',
        soaip => '192.168.42.42',
        a     => [{'name' => 'ns1', 'ip' => '192.168.42.42'}, {'name' => 'mx2', 'ip' => '192.168.42.42'}, {'name' => 'ftp', 'ip' => '192.168.42.43'}],
        mx    => [{'priority' => '10', 'name' => 'mx2.example.com.'}],
        ns    => [{'name' => 'ns1.example.com.'}],
        cname => [{'cname' => 'puet', 'original' => 'ns1'}],
    }