Add middleware/erratic (#471)

This middleware allows playing with responses. Only one type is
implemented: it allows you to drop queries. I.e. withhold the response
from the client.

middleware/erratic/setup_test.go

@@ -0,0 +1,28 @@
+package erratic
+
+import (
+	"testing"
+
+	"github.com/mholt/caddy"
+)
+
+func TestSetupWhoami(t *testing.T) {
+	c := caddy.NewTestController("dns", `erratic {
+		drop
+	}`)
+	if err := setupErratic(c); err != nil {
+		t.Fatalf("Test 1, expected no errors, but got: %q", err)
+	}
+
+	c = caddy.NewTestController("dns", `erratic`)
+	if err := setupErratic(c); err != nil {
+		t.Fatalf("Test 2, expected no errors, but got: %q", err)
+	}
+
+	c = caddy.NewTestController("dns", `erratic {
+		drop -1
+	}`)
+	if err := setupErratic(c); err == nil {
+		t.Fatalf("Test 4, expected errors, but got: %q", err)
+	}
+}