[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/.travis.yml b/vendor/sigs.k8s.io/yaml/.travis.yml
new file mode 100644
index 0000000..03ddc73
--- /dev/null
+++ b/vendor/sigs.k8s.io/yaml/.travis.yml
@@ -0,0 +1,14 @@
+language: go
+dist: xenial
+go:
+  - 1.9.x
+  - 1.10.x
+  - 1.11.x
+script:
+  - go get -t -v ./...
+  - diff -u <(echo -n) <(gofmt -d .)
+  - diff -u <(echo -n) <(golint $(go list -e ./...) | grep -v YAMLToJSON)
+  - go tool vet .
+  - go test -v -race ./...
+install:
+  - go get golang.org/x/lint/golint