[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/json-iterator/go/build.sh b/vendor/github.com/json-iterator/go/build.sh
new file mode 100644
index 0000000..b45ef68
--- /dev/null
+++ b/vendor/github.com/json-iterator/go/build.sh
@@ -0,0 +1,12 @@
+#!/bin/bash
+set -e
+set -x
+
+if [ ! -d /tmp/build-golang/src/github.com/json-iterator ]; then
+    mkdir -p /tmp/build-golang/src/github.com/json-iterator
+    ln -s $PWD /tmp/build-golang/src/github.com/json-iterator/go
+fi
+export GOPATH=/tmp/build-golang
+go get -u github.com/golang/dep/cmd/dep
+cd /tmp/build-golang/src/github.com/json-iterator/go
+exec $GOPATH/bin/dep ensure -update