WORKDIR set cmd

Signed-off-by: John Howard <jhoward@microsoft.com>

builder/dockerfile/dispatchers.go

@@ -290,6 +290,17 @@ func workdir(b *Builder, args []string, attributes map[string]bool, original str
 		return nil
 	}
 	b.runConfig.Image = b.image
+
+	cmd := b.runConfig.Cmd
+	b.runConfig.Cmd = strslice.StrSlice(append(getShell(b.runConfig), fmt.Sprintf("#(nop) WORKDIR %s", b.runConfig.WorkingDir)))
+	defer func(cmd strslice.StrSlice) { b.runConfig.Cmd = cmd }(cmd)
+
+	if hit, err := b.probeCache(); err != nil {
+		return err
+	} else if hit {
+		return nil
+	}
+
 	container, err := b.docker.ContainerCreate(types.ContainerCreateConfig{Config: b.runConfig}, true)
 	if err != nil {
 		return err