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/imdario/mergo/merge.go

@@ -0,0 +1,99 @@
+// Copyright 2013 Dario Castañé. All rights reserved.
+// 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.
+
+// Based on src/pkg/reflect/deepequal.go from official
+// golang's stdlib.
+
+package mergo
+
+import (
+	"reflect"
+)
+
+// Traverses recursively both values, assigning src's fields values to dst.
+// The map argument tracks comparisons that have already been seen, which allows
+// short circuiting on recursive types.
+func deepMerge(dst, src reflect.Value, visited map[uintptr]*visit, depth int) (err error) {
+	if !src.IsValid() {
+		return
+	}
+	if dst.CanAddr() {
+		addr := dst.UnsafeAddr()
+		h := 17 * addr
+		seen := visited[h]
+		typ := dst.Type()
+		for p := seen; p != nil; p = p.next {
+			if p.ptr == addr && p.typ == typ {
+				return nil
+			}
+		}
+		// Remember, remember...
+		visited[h] = &visit{addr, typ, seen}
+	}
+	switch dst.Kind() {
+	case reflect.Struct:
+		for i, n := 0, dst.NumField(); i < n; i++ {
+			if err = deepMerge(dst.Field(i), src.Field(i), visited, depth+1); err != nil {
+				return
+			}
+		}
+	case reflect.Map:
+		for _, key := range src.MapKeys() {
+			srcElement := src.MapIndex(key)
+			if !srcElement.IsValid() {
+				continue
+			}
+			dstElement := dst.MapIndex(key)
+			switch reflect.TypeOf(srcElement.Interface()).Kind() {
+			case reflect.Struct:
+				fallthrough
+			case reflect.Map:
+				if err = deepMerge(dstElement, srcElement, visited, depth+1); err != nil {
+					return
+				}
+			}
+			if !dstElement.IsValid() {
+				dst.SetMapIndex(key, srcElement)
+			}
+		}
+	case reflect.Ptr:
+		fallthrough
+	case reflect.Interface:
+		if src.IsNil() {
+			break
+		} else if dst.IsNil() {
+			if dst.CanSet() && isEmptyValue(dst) {
+				dst.Set(src)
+			}
+		} else if err = deepMerge(dst.Elem(), src.Elem(), visited, depth+1); err != nil {
+			return
+		}
+	default:
+		if dst.CanSet() && !isEmptyValue(src) {
+			dst.Set(src)
+		}
+	}
+	return
+}
+
+// Merge sets fields' values in dst from src if they have a zero
+// value of their type.
+// dst and src must be valid same-type structs and dst must be
+// a pointer to struct.
+// It won't merge unexported (private) fields and will do recursively
+// any exported field.
+func Merge(dst, src interface{}) error {
+	var (
+		vDst, vSrc reflect.Value
+		err        error
+	)
+	if vDst, vSrc, err = resolveValues(dst, src); err != nil {
+		return err
+	}
+	if vDst.Type() != vSrc.Type() {
+		return ErrDifferentArgumentsTypes
+	}
+	return deepMerge(vDst, vSrc, make(map[uintptr]*visit), 0)
+}