test: skip . files in directory

Xcode generates ._foo.go files.

R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/5786055

test/run.go

@@ -147,7 +147,7 @@ func goFiles(dir string) []string {
 	check(err)
 	names := []string{}
 	for _, name := range dirnames {
-		if strings.HasSuffix(name, ".go") {
+		if !strings.HasPrefix(name, ".") && strings.HasSuffix(name, ".go") {
 			names = append(names, name)
 		}
 	}