Revert vendor directory to support old golang (GOPATH mode)

gomodule is still in progress to migrate for now, hence multus
team decide to keep vendor directory to support build without
gomodule.

vendor/github.com/spf13/pflag/golangflag.go

@@ -0,0 +1,105 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package pflag
+
+import (
+	goflag "flag"
+	"reflect"
+	"strings"
+)
+
+// flagValueWrapper implements pflag.Value around a flag.Value.  The main
+// difference here is the addition of the Type method that returns a string
+// name of the type.  As this is generally unknown, we approximate that with
+// reflection.
+type flagValueWrapper struct {
+	inner    goflag.Value
+	flagType string
+}
+
+// We are just copying the boolFlag interface out of goflag as that is what
+// they use to decide if a flag should get "true" when no arg is given.
+type goBoolFlag interface {
+	goflag.Value
+	IsBoolFlag() bool
+}
+
+func wrapFlagValue(v goflag.Value) Value {
+	// If the flag.Value happens to also be a pflag.Value, just use it directly.
+	if pv, ok := v.(Value); ok {
+		return pv
+	}
+
+	pv := &flagValueWrapper{
+		inner: v,
+	}
+
+	t := reflect.TypeOf(v)
+	if t.Kind() == reflect.Interface || t.Kind() == reflect.Ptr {
+		t = t.Elem()
+	}
+
+	pv.flagType = strings.TrimSuffix(t.Name(), "Value")
+	return pv
+}
+
+func (v *flagValueWrapper) String() string {
+	return v.inner.String()
+}
+
+func (v *flagValueWrapper) Set(s string) error {
+	return v.inner.Set(s)
+}
+
+func (v *flagValueWrapper) Type() string {
+	return v.flagType
+}
+
+// PFlagFromGoFlag will return a *pflag.Flag given a *flag.Flag
+// If the *flag.Flag.Name was a single character (ex: `v`) it will be accessiblei
+// with both `-v` and `--v` in flags. If the golang flag was more than a single
+// character (ex: `verbose`) it will only be accessible via `--verbose`
+func PFlagFromGoFlag(goflag *goflag.Flag) *Flag {
+	// Remember the default value as a string; it won't change.
+	flag := &Flag{
+		Name:  goflag.Name,
+		Usage: goflag.Usage,
+		Value: wrapFlagValue(goflag.Value),
+		// Looks like golang flags don't set DefValue correctly  :-(
+		//DefValue: goflag.DefValue,
+		DefValue: goflag.Value.String(),
+	}
+	// Ex: if the golang flag was -v, allow both -v and --v to work
+	if len(flag.Name) == 1 {
+		flag.Shorthand = flag.Name
+	}
+	if fv, ok := goflag.Value.(goBoolFlag); ok && fv.IsBoolFlag() {
+		flag.NoOptDefVal = "true"
+	}
+	return flag
+}
+
+// AddGoFlag will add the given *flag.Flag to the pflag.FlagSet
+func (f *FlagSet) AddGoFlag(goflag *goflag.Flag) {
+	if f.Lookup(goflag.Name) != nil {
+		return
+	}
+	newflag := PFlagFromGoFlag(goflag)
+	f.AddFlag(newflag)
+}
+
+// AddGoFlagSet will add the given *flag.FlagSet to the pflag.FlagSet
+func (f *FlagSet) AddGoFlagSet(newSet *goflag.FlagSet) {
+	if newSet == nil {
+		return
+	}
+	newSet.VisitAll(func(goflag *goflag.Flag) {
+		f.AddGoFlag(goflag)
+	})
+	if f.addedGoFlagSets == nil {
+		f.addedGoFlagSets = make([]*goflag.FlagSet, 0)
+	}
+	f.addedGoFlagSets = append(f.addedGoFlagSets, newSet)
+}