[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/grpc-ecosystem/grpc-gateway/internal/BUILD.bazel b/vendor/github.com/grpc-ecosystem/grpc-gateway/internal/BUILD.bazel
new file mode 100644
index 0000000..76cafe6
--- /dev/null
+++ b/vendor/github.com/grpc-ecosystem/grpc-gateway/internal/BUILD.bazel
@@ -0,0 +1,22 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+load("@io_bazel_rules_go//proto:def.bzl", "go_proto_library")
+
+package(default_visibility = ["//visibility:public"])
+
+proto_library(
+    name = "internal_proto",
+    srcs = ["stream_chunk.proto"],
+    deps = ["@com_google_protobuf//:any_proto"],
+)
+
+go_proto_library(
+    name = "internal_go_proto",
+    importpath = "github.com/grpc-ecosystem/grpc-gateway/internal",
+    proto = ":internal_proto",
+)
+
+go_library(
+    name = "go_default_library",
+    embed = [":internal_go_proto"],
+    importpath = "github.com/grpc-ecosystem/grpc-gateway/internal",
+)