[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/fileutil/lock_windows.go b/vendor/go.etcd.io/etcd/pkg/fileutil/lock_windows.go
new file mode 100644
index 0000000..b181723
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/pkg/fileutil/lock_windows.go
@@ -0,0 +1,125 @@
+// 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.
+
+// +build windows
+
+package fileutil
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+var (
+	modkernel32    = syscall.NewLazyDLL("kernel32.dll")
+	procLockFileEx = modkernel32.NewProc("LockFileEx")
+
+	errLocked = errors.New("The process cannot access the file because another process has locked a portion of the file.")
+)
+
+const (
+	// https://msdn.microsoft.com/en-us/library/windows/desktop/aa365203(v=vs.85).aspx
+	LOCKFILE_EXCLUSIVE_LOCK   = 2
+	LOCKFILE_FAIL_IMMEDIATELY = 1
+
+	// see https://msdn.microsoft.com/en-us/library/windows/desktop/ms681382(v=vs.85).aspx
+	errLockViolation syscall.Errno = 0x21
+)
+
+func TryLockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
+	f, err := open(path, flag, perm)
+	if err != nil {
+		return nil, err
+	}
+	if err := lockFile(syscall.Handle(f.Fd()), LOCKFILE_FAIL_IMMEDIATELY); err != nil {
+		f.Close()
+		return nil, err
+	}
+	return &LockedFile{f}, nil
+}
+
+func LockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
+	f, err := open(path, flag, perm)
+	if err != nil {
+		return nil, err
+	}
+	if err := lockFile(syscall.Handle(f.Fd()), 0); err != nil {
+		f.Close()
+		return nil, err
+	}
+	return &LockedFile{f}, nil
+}
+
+func open(path string, flag int, perm os.FileMode) (*os.File, error) {
+	if path == "" {
+		return nil, fmt.Errorf("cannot open empty filename")
+	}
+	var access uint32
+	switch flag {
+	case syscall.O_RDONLY:
+		access = syscall.GENERIC_READ
+	case syscall.O_WRONLY:
+		access = syscall.GENERIC_WRITE
+	case syscall.O_RDWR:
+		access = syscall.GENERIC_READ | syscall.GENERIC_WRITE
+	case syscall.O_WRONLY | syscall.O_CREAT:
+		access = syscall.GENERIC_ALL
+	default:
+		panic(fmt.Errorf("flag %v is not supported", flag))
+	}
+	fd, err := syscall.CreateFile(&(syscall.StringToUTF16(path)[0]),
+		access,
+		syscall.FILE_SHARE_READ|syscall.FILE_SHARE_WRITE|syscall.FILE_SHARE_DELETE,
+		nil,
+		syscall.OPEN_ALWAYS,
+		syscall.FILE_ATTRIBUTE_NORMAL,
+		0)
+	if err != nil {
+		return nil, err
+	}
+	return os.NewFile(uintptr(fd), path), nil
+}
+
+func lockFile(fd syscall.Handle, flags uint32) error {
+	var flag uint32 = LOCKFILE_EXCLUSIVE_LOCK
+	flag |= flags
+	if fd == syscall.InvalidHandle {
+		return nil
+	}
+	err := lockFileEx(fd, flag, 1, 0, &syscall.Overlapped{})
+	if err == nil {
+		return nil
+	} else if err.Error() == errLocked.Error() {
+		return ErrLocked
+	} else if err != errLockViolation {
+		return err
+	}
+	return nil
+}
+
+func lockFileEx(h syscall.Handle, flags, locklow, lockhigh uint32, ol *syscall.Overlapped) (err error) {
+	var reserved uint32 = 0
+	r1, _, e1 := syscall.Syscall6(procLockFileEx.Addr(), 6, uintptr(h), uintptr(flags), uintptr(reserved), uintptr(locklow), uintptr(lockhigh), uintptr(unsafe.Pointer(ol)))
+	if r1 == 0 {
+		if e1 != 0 {
+			err = error(e1)
+		} else {
+			err = syscall.EINVAL
+		}
+	}
+	return err
+}