[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/dgrijalva/jwt-go/.travis.yml b/vendor/github.com/dgrijalva/jwt-go/.travis.yml
new file mode 100644
index 0000000..1027f56
--- /dev/null
+++ b/vendor/github.com/dgrijalva/jwt-go/.travis.yml
@@ -0,0 +1,13 @@
+language: go
+
+script:
+    - go vet ./...
+    - go test -v ./...
+
+go:
+  - 1.3
+  - 1.4
+  - 1.5
+  - 1.6
+  - 1.7
+  - tip