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/github.com/Shopify/sarama/add_offsets_to_txn_response.go b/demo_test/vendor/github.com/Shopify/sarama/add_offsets_to_txn_response.go
new file mode 100644
index 0000000..c88c1f8
--- /dev/null
+++ b/demo_test/vendor/github.com/Shopify/sarama/add_offsets_to_txn_response.go
@@ -0,0 +1,45 @@
+package sarama
+
+import (
+	"time"
+)
+
+//AddOffsetsToTxnResponse is a response type for adding offsets to txns
+type AddOffsetsToTxnResponse struct {
+	ThrottleTime time.Duration
+	Err          KError
+}
+
+func (a *AddOffsetsToTxnResponse) encode(pe packetEncoder) error {
+	pe.putInt32(int32(a.ThrottleTime / time.Millisecond))
+	pe.putInt16(int16(a.Err))
+	return nil
+}
+
+func (a *AddOffsetsToTxnResponse) decode(pd packetDecoder, version int16) (err error) {
+	throttleTime, err := pd.getInt32()
+	if err != nil {
+		return err
+	}
+	a.ThrottleTime = time.Duration(throttleTime) * time.Millisecond
+
+	kerr, err := pd.getInt16()
+	if err != nil {
+		return err
+	}
+	a.Err = KError(kerr)
+
+	return nil
+}
+
+func (a *AddOffsetsToTxnResponse) key() int16 {
+	return 25
+}
+
+func (a *AddOffsetsToTxnResponse) version() int16 {
+	return 0
+}
+
+func (a *AddOffsetsToTxnResponse) requiredVersion() KafkaVersion {
+	return V0_11_0_0
+}