Create a maintenance mutex skeleton within luci-go

mmutex/cmd/mmutex/main.go

Index: mmutex/cmd/mmutex/main.go
diff --git a/mmutex/cmd/mmutex/main.go b/mmutex/cmd/mmutex/main.go
new file mode 100644
index 0000000000000000000000000000000000000000..d61b202902035f014f3edb4f856c6365c1465583
--- /dev/null
+++ b/mmutex/cmd/mmutex/main.go
@@ -0,0 +1,9 @@
+// Copyright 2017 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package main
+
+func main() {
+	// TODO(charliea): Write the command line interface.
+}