[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/sigs.k8s.io/yaml/.gitignore b/vendor/sigs.k8s.io/yaml/.gitignore
new file mode 100644
index 0000000..e256a31
--- /dev/null
+++ b/vendor/sigs.k8s.io/yaml/.gitignore
@@ -0,0 +1,20 @@
+# OSX leaves these everywhere on SMB shares
+._*
+
+# Eclipse files
+.classpath
+.project
+.settings/**
+
+# Emacs save files
+*~
+
+# Vim-related files
+[._]*.s[a-w][a-z]
+[._]s[a-w][a-z]
+*.un~
+Session.vim
+.netrwhist
+
+# Go test binaries
+*.test