[cipd] Move ValidateRoot to common package

cipd/client/cipd/ensure/item_parsers.go

 // 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 ensure
 
 import (
         "fmt"
         "net/url"
+
+        "github.com/luci/luci-go/cipd/client/cipd/common"
 )
 
 // an itemParser should parse the value from `val`, and update s or
 // f accordingly, returning an error if needed.
 type itemParser func(s *itemParserState, f *File, val string) error
 
 // itemParserState is the state object shared between the item parsers and the
 // main ParseFile implementation.
 type itemParserState struct {
         curRoot string
 }
 
 func rootParser(s *itemParserState, _ *File, val string) error {
-        if err := ValidateRoot(val); err != nil {
+        if err := common.ValidateRoot(val); err != nil {
                 return err
         }
         s.curRoot = val
         return nil
 }
 
 func serviceURLParser(_ *itemParserState, f *File, val string) error {
         if f.ServiceURL != "" {
                 return fmt.Errorf("$ServiceURL may only be set once per file")
         }
         if _, err := url.Parse(val); err != nil {
                 return fmt.Errorf("expecting '$ServiceURL <url>' but url is invalid: %s", err)
         }
         f.ServiceURL = val
         return nil
 }
 
 // itemParsers is the main way that the ensure file format is extended. If you
 // need to add a new setting or directive, please add an appropriate function
 // above and then add it to this map.
 var itemParsers = map[string]itemParser{
         "@root":       rootParser,
         "$serviceurl": serviceURLParser,
 }