Improve caching of non-response

[matsduf]

At the time of writing, when querying z.arin.net, there is no response from at least many ISPs in Sweden:

 $ dig -4 @z.arin.net 109.32.239.216.in-addr.arpa ptr

; <<>> DiG 9.10.6 <<>> -4 @z.arin.net 109.32.239.216.in-addr.arpa ptr
; (1 server found)
;; global options: +cmd
;; connection timed out; no servers could be reached

$ dig -6 @z.arin.net 109.32.239.216.in-addr.arpa ptr

; <<>> DiG 9.10.6 <<>> -6 @z.arin.net 109.32.239.216.in-addr.arpa ptr
; (1 server found)
;; global options: +cmd
;; connection timed out; no servers could be reached

When testing "dn.se" with zonemaster-cli it sends PTR query 8 times to the IPv4 address and 8 times to the IPv6 address even though there was no response already first time. We should improve caching of no response.

$ zonemaster-cli dn.se --level debug --test address | grep "because of network error"
  10.84 DEBUG    DNS query to z.arin.net/199.180.180.63 for d.6.0.0.0.0.0.0.0.0.0.0.0.0.0.0.2.3.0.0.2.0.8.4.0.6.8.4.1.0.0.2.ip6.arpa/PTR/IN failed with error: Could not send or receive, because of network error.
  20.91 DEBUG    DNS query to z.arin.net/2001:500:f0::63 for d.6.0.0.0.0.0.0.0.0.0.0.0.0.0.0.2.3.0.0.2.0.8.4.0.6.8.4.1.0.0.2.ip6.arpa/PTR/IN failed with error: Could not send or receive, because of network error.
  31.21 DEBUG    DNS query to z.arin.net/199.180.180.63 for 109.32.239.216.in-addr.arpa/PTR/IN failed with error: Could not send or receive, because of network error.
  41.24 DEBUG    DNS query to z.arin.net/2001:500:f0::63 for 109.32.239.216.in-addr.arpa/PTR/IN failed with error: Could not send or receive, because of network error.
  51.34 DEBUG    DNS query to z.arin.net/199.180.180.63 for d.6.0.0.0.0.0.0.0.0.0.0.0.0.0.0.4.3.0.0.2.0.8.4.0.6.8.4.1.0.0.2.ip6.arpa/PTR/IN failed with error: Could not send or receive, because of network error.
  61.41 DEBUG    DNS query to z.arin.net/2001:500:f0::63 for d.6.0.0.0.0.0.0.0.0.0.0.0.0.0.0.4.3.0.0.2.0.8.4.0.6.8.4.1.0.0.2.ip6.arpa/PTR/IN failed with error: Could not send or receive, because of network error.
  71.51 DEBUG    DNS query to z.arin.net/199.180.180.63 for 109.34.239.216.in-addr.arpa/PTR/IN failed with error: Could not send or receive, because of network error.
  81.54 DEBUG    DNS query to z.arin.net/2001:500:f0::63 for 109.34.239.216.in-addr.arpa/PTR/IN failed with error: Could not send or receive, because of network error.
  91.64 DEBUG    DNS query to z.arin.net/199.180.180.63 for d.6.0.0.0.0.0.0.0.0.0.0.0.0.0.0.6.3.0.0.2.0.8.4.0.6.8.4.1.0.0.2.ip6.arpa/PTR/IN failed with error: Could not send or receive, because of network error.
 101.70 DEBUG    DNS query to z.arin.net/2001:500:f0::63 for d.6.0.0.0.0.0.0.0.0.0.0.0.0.0.0.6.3.0.0.2.0.8.4.0.6.8.4.1.0.0.2.ip6.arpa/PTR/IN failed with error: Could not send or receive, because of network error.
 111.80 DEBUG    DNS query to z.arin.net/199.180.180.63 for 109.36.239.216.in-addr.arpa/PTR/IN failed with error: Could not send or receive, because of network error.
 121.82 DEBUG    DNS query to z.arin.net/2001:500:f0::63 for 109.36.239.216.in-addr.arpa/PTR/IN failed with error: Could not send or receive, because of network error.
 131.93 DEBUG    DNS query to z.arin.net/199.180.180.63 for d.6.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.3.0.0.2.0.8.4.0.6.8.4.1.0.0.2.ip6.arpa/PTR/IN failed with error: Could not send or receive, because of network error.
 141.94 DEBUG    DNS query to z.arin.net/2001:500:f0::63 for d.6.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.3.0.0.2.0.8.4.0.6.8.4.1.0.0.2.ip6.arpa/PTR/IN failed with error: Could not send or receive, because of network error.
 152.07 DEBUG    DNS query to z.arin.net/199.180.180.63 for 109.38.239.216.in-addr.arpa/PTR/IN failed with error: Could not send or receive, because of network error.
 162.09 DEBUG    DNS query to z.arin.net/2001:500:f0::63 for 109.38.239.216.in-addr.arpa/PTR/IN failed with error: Could not send or receive, because of network error.