[VOL-2193] Create mocks for Kafka Client and Etcd

This commit consists of:
1) A kafka client mock that implements the kafka client interface
under voltha-lib-go/pkg/kafka/client.go
2) An embedded Etcd server that runs in-process and represents an
Etcd server.

Change-Id: I52a36132568e08c596bb4136918bebcb654a3b99
diff --git a/vendor/github.com/sirupsen/logrus/go.mod b/vendor/github.com/sirupsen/logrus/go.mod
new file mode 100644
index 0000000..94574cc
--- /dev/null
+++ b/vendor/github.com/sirupsen/logrus/go.mod
@@ -0,0 +1,11 @@
+module github.com/sirupsen/logrus
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/konsorten/go-windows-terminal-sequences v1.0.1
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/stretchr/objx v0.1.1 // indirect
+	github.com/stretchr/testify v1.2.2
+	golang.org/x/crypto v0.0.0-20180904163835-0709b304e793
+	golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33
+)