reverse zone: fix Normalize (#4621)

Make normalize return multiple "hosts" (= reverse zones) when a
non-octet boundary cidr is given.

Added pkg/cidr package that holds the cidr calculation routines; felt
they didn't really fit dnsutil.

This change means the IPNet return parameter isn't needed, the hosts are
all correct. The tests that tests this is also removed: TestSplitHostPortReverse
The fallout was that zoneAddr _also_ doesn't need the IPNet member, that
in turn make it visible that zoneAddr in address.go duplicated a bunch
of stuff from register.go; removed/refactored that too.

Created a plugin.OriginsFromArgsOrServerBlock to help plugins do the
right things, by consuming ZONE arguments; this now expands reverse
zones correctly. This is mostly mechanical.

Remove the reverse test in plugin/kubernetes which is a copy-paste from
a core test (which has since been fixed).

Remove MustNormalize as it has no plugin users.

This change is not backwards compatible to plugins that have a ZONE
argument that they parse in the setup util.

All in-tree plugins have been updated.

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/auto/setup.go

@@ -87,16 +87,8 @@ func autoParse(c *caddy.Controller) (Auto, error) {
 
 	for c.Next() {
 		// auto [ZONES...]
-		a.Zones.origins = make([]string, len(c.ServerBlockKeys))
-		copy(a.Zones.origins, c.ServerBlockKeys)
-
 		args := c.RemainingArgs()
-		if len(args) > 0 {
-			a.Zones.origins = args
-		}
-		for i := range a.Zones.origins {
-			a.Zones.origins[i] = plugin.Host(a.Zones.origins[i]).Normalize()
-		}
+		a.Zones.origins = plugin.OriginsFromArgsOrServerBlock(args, c.ServerBlockKeys)
 		a.loader.upstream = upstream.New()
 
 		for c.NextBlock() {