Add pkg/fall for Fallthrough (#1355)

* Add pkg/fall for Fallthrough

Move this into it's own package to facilitate tests. Important bug
was fixed: make the names fully qualified.

Add fall package to hosts, reverse, etcd, and fix kubernetes and any
tests. The k8s tests are still as-is, might need a future cleanup.

plugin/pkg/fall/fall_test.go

@@ -0,0 +1,48 @@
+package fall
+
+import "testing"
+
+func TestIsNil(t *testing.T) {
+	var f *F
+	if !f.IsNil() {
+		t.Errorf("F should be nil")
+	}
+}
+
+func TestIsZero(t *testing.T) {
+	f := New()
+	if !f.IsZero() {
+		t.Errorf("F should be zero")
+	}
+}
+
+func TestFallThroughExample(t *testing.T) {
+	if !Example.Through("example.org.") {
+		t.Errorf("example.org. should fall through")
+	}
+	if Example.Through("example.net.") {
+		t.Errorf("example.net. should not fall through")
+	}
+}
+
+func TestFallthrough(t *testing.T) {
+	var fall *F
+	if fall.Through("foo.com.") {
+		t.Errorf("Expected false, got true for nil fallthrough")
+	}
+
+	fall = New()
+	if !fall.Through("foo.net.") {
+		t.Errorf("Expected true, got false for all zone fallthrough")
+	}
+
+	fall.SetZones([]string{"foo.com", "bar.com"})
+
+	if fall.Through("foo.net.") {
+		t.Errorf("Expected false, got true for non-matching fallthrough zone")
+	}
+
+	if !fall.Through("bar.com.") {
+		t.Errorf("Expected true, got false for matching fallthrough zone")
+	}
+}