[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/etcd/pkg/runtime/fds_linux.go b/vendor/go.etcd.io/etcd/pkg/runtime/fds_linux.go
new file mode 100644
index 0000000..8e9359d
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/pkg/runtime/fds_linux.go
@@ -0,0 +1,37 @@
+// Copyright 2015 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package runtime implements utility functions for runtime systems.
+package runtime
+
+import (
+	"io/ioutil"
+	"syscall"
+)
+
+func FDLimit() (uint64, error) {
+	var rlimit syscall.Rlimit
+	if err := syscall.Getrlimit(syscall.RLIMIT_NOFILE, &rlimit); err != nil {
+		return 0, err
+	}
+	return rlimit.Cur, nil
+}
+
+func FDUsage() (uint64, error) {
+	fds, err := ioutil.ReadDir("/proc/self/fd")
+	if err != nil {
+		return 0, err
+	}
+	return uint64(len(fds)), nil
+}