add vendoring with go dep

vendor/github.com/vmware/govmomi/govc/flags/common.go

@@ -0,0 +1,38 @@
+/*
+Copyright (c) 2015-2016 VMware, Inc. All Rights Reserved.
+
+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 flags
+
+import "sync"
+
+// Key type for storing flag instances in a context.Context.
+type flagKey string
+
+// Type to help flags out with only registering/processing once.
+type common struct {
+	register sync.Once
+	process  sync.Once
+}
+
+func (c *common) RegisterOnce(fn func()) {
+	c.register.Do(fn)
+}
+
+func (c *common) ProcessOnce(fn func() error) (err error) {
+	c.process.Do(func() {
+		err = fn()
+	})
+	return err
+}