mw/autopath: integration test with erratic (#930)

Add integration test with erratic. For this erratic now also returns an
autopath searchpath. This tests the whole chain; i.e registring a
searchfunction and calling that from autopath.

This tests does a autopathing domain and a non-autopathing one.

middleware/erratic/autopath.go

@@ -0,0 +1,8 @@
+package erratic
+
+import "github.com/coredns/coredns/request"
+
+// AutoPath implements the AutoPathFunc call from the autopath middleware.
+func (e *Erratic) AutoPath(state request.Request) []string {
+	return []string{"a.example.org.", "b.example.org.", ""}
+}