[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/soheilhy/cmux/.travis.yml b/vendor/github.com/soheilhy/cmux/.travis.yml
new file mode 100644
index 0000000..4bc48e0
--- /dev/null
+++ b/vendor/github.com/soheilhy/cmux/.travis.yml
@@ -0,0 +1,29 @@
+language: go
+
+go:
+  - 1.6
+  - 1.7
+  - 1.8
+  - tip
+
+matrix:
+  allow_failures:
+    - go: tip
+
+gobuild_args: -race
+
+before_install:
+  - if [[ $TRAVIS_GO_VERSION == 1.6* ]]; then go get -u github.com/kisielk/errcheck; fi
+  - if [[ $TRAVIS_GO_VERSION == 1.6* ]]; then go get -u github.com/golang/lint/golint; fi
+
+before_script:
+  - '! gofmt -s -l . | read'
+  - echo $TRAVIS_GO_VERSION
+  - if [[ $TRAVIS_GO_VERSION == 1.6* ]]; then golint ./...; fi
+  - if [[ $TRAVIS_GO_VERSION == 1.6* ]]; then errcheck ./...; fi
+  - if [[ $TRAVIS_GO_VERSION == 1.6* ]]; then go tool vet .; fi
+  - if [[ $TRAVIS_GO_VERSION == 1.6* ]]; then go tool vet --shadow .; fi
+
+script:
+  - go test -bench . -v ./...
+  - go test -race -bench . -v ./...