builder/parser: Make use of builder/command

Signed-off-by: Ahmet Alp Balkan <ahmetalpbalkan@gmail.com>

builder/parser/parser.go

@@ -7,6 +7,8 @@ import (
 	"regexp"
 	"strings"
 	"unicode"
+
+	"github.com/docker/docker/builder/command"
 )
 
 // Node is a structure used to represent a parse tree.
@@ -44,20 +46,20 @@ func init() {
 	// functions. Errors are propagated up by Parse() and the resulting AST can
 	// be incorporated directly into the existing AST as a next.
 	dispatch = map[string]func(string) (*Node, map[string]bool, error){
-		"user":       parseString,
-		"onbuild":    parseSubCommand,
-		"workdir":    parseString,
-		"env":        parseEnv,
-		"maintainer": parseString,
-		"from":       parseString,
-		"add":        parseMaybeJSONToList,
-		"copy":       parseMaybeJSONToList,
-		"run":        parseMaybeJSON,
-		"cmd":        parseMaybeJSON,
-		"entrypoint": parseMaybeJSON,
-		"expose":     parseStringsWhitespaceDelimited,
-		"volume":     parseMaybeJSONToList,
-		"insert":     parseIgnore,
+		command.User:       parseString,
+		command.Onbuild:    parseSubCommand,
+		command.Workdir:    parseString,
+		command.Env:        parseEnv,
+		command.Maintainer: parseString,
+		command.From:       parseString,
+		command.Add:        parseMaybeJSONToList,
+		command.Copy:       parseMaybeJSONToList,
+		command.Run:        parseMaybeJSON,
+		command.Cmd:        parseMaybeJSON,
+		command.Entrypoint: parseMaybeJSON,
+		command.Expose:     parseStringsWhitespaceDelimited,
+		command.Volume:     parseMaybeJSONToList,
+		command.Insert:     parseIgnore,
 	}
 }