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/metadata/setup.go

@@ -34,19 +34,8 @@ func setup(c *caddy.Controller) error {
 func metadataParse(c *caddy.Controller) (*Metadata, error) {
 	m := &Metadata{}
 	c.Next()
-	zones := c.RemainingArgs()
 
-	if len(zones) != 0 {
-		m.Zones = zones
-		for i := 0; i < len(m.Zones); i++ {
-			m.Zones[i] = plugin.Host(m.Zones[i]).Normalize()
-		}
-	} else {
-		m.Zones = make([]string, len(c.ServerBlockKeys))
-		for i := 0; i < len(c.ServerBlockKeys); i++ {
-			m.Zones[i] = plugin.Host(c.ServerBlockKeys[i]).Normalize()
-		}
-	}
+	m.Zones = plugin.OriginsFromArgsOrServerBlock(c.RemainingArgs(), c.ServerBlockKeys)
 
 	if c.NextBlock() || c.Next() {
 		return nil, plugin.Error("metadata", c.ArgErr())