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/grpc/setup.go

@@ -56,7 +56,7 @@ func parseStanza(c *caddy.Controller) (*GRPC, error) {
 	if !c.Args(&g.from) {
 		return g, c.ArgErr()
 	}
-	g.from = plugin.Host(g.from).Normalize()
+	g.from = plugin.Host(g.from).Normalize()[0] // only the first is used.
 
 	to := c.RemainingArgs()
 	if len(to) == 0 {
@@ -100,9 +100,8 @@ func parseBlock(c *caddy.Controller, g *GRPC) error {
 			return c.ArgErr()
 		}
 		for i := 0; i < len(ignore); i++ {
-			ignore[i] = plugin.Host(ignore[i]).Normalize()
+			g.ignored = append(g.ignored, plugin.Host(ignore[i]).Normalize()...)
 		}
-		g.ignored = ignore
 	case "tls":
 		args := c.RemainingArgs()
 		if len(args) > 3 {