Move kustomize main to cmd directory.

cmd/kustomize/main.go

@@ -0,0 +1,17 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package main
+
+import (
+	"os"
+
+	"sigs.k8s.io/kustomize/pkg/commands"
+)
+
+func main() {
+	if err := commands.NewDefaultCommand().Execute(); err != nil {
+		os.Exit(1)
+	}
+	os.Exit(0)
+}