[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/go.etcd.io/bbolt/.travis.yml b/vendor/go.etcd.io/bbolt/.travis.yml
new file mode 100644
index 0000000..a60300c
--- /dev/null
+++ b/vendor/go.etcd.io/bbolt/.travis.yml
@@ -0,0 +1,17 @@
+language: go
+go_import_path: go.etcd.io/bbolt
+
+sudo: false
+
+go:
+- 1.11
+
+before_install:
+- go get -v honnef.co/go/tools/...
+- go get -v github.com/kisielk/errcheck
+
+script:
+- make fmt
+- make test
+- make race
+# - make errcheck