SEBA-902 single-olt tests;
Pin protoc-gen-go to 1.3.2 to resolve compatibility issue;
Run go mod tidy / go mod vendor on importer;
Add Go Module support to demotest

Change-Id: Ifde824fc9a6317b0adc1e12bea54ee1f9b788906
diff --git a/demo_test/vendor/google.golang.org/protobuf/encoding/prototext/doc.go b/demo_test/vendor/google.golang.org/protobuf/encoding/prototext/doc.go
new file mode 100644
index 0000000..162b4f9
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/protobuf/encoding/prototext/doc.go
@@ -0,0 +1,7 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package prototext marshals and unmarshals protocol buffer messages as the
+// textproto format.
+package prototext