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/golang.org/x/sys/unix/syscall_darwin_amd64.1_11.go b/demo_test/vendor/golang.org/x/sys/unix/syscall_darwin_amd64.1_11.go
new file mode 100644
index 0000000..68ebd6f
--- /dev/null
+++ b/demo_test/vendor/golang.org/x/sys/unix/syscall_darwin_amd64.1_11.go
@@ -0,0 +1,9 @@
+// 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.
+
+// +build darwin,amd64,!go1.12
+
+package unix
+
+//sys  Getdirentries(fd int, buf []byte, basep *uintptr) (n int, err error) = SYS_GETDIRENTRIES64