os: check setStickyBit error in mkdir

If an error occurs, delete the newly created directory.

Change-Id: I97e960d24af32f027fb23d5ce3f61959e73f6fb0
Reviewed-on: https://go-review.googlesource.com/115715
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/os/file.go

@@ -221,7 +221,12 @@ func Mkdir(name string, perm FileMode) error {
 
 	// mkdir(2) itself won't handle the sticky bit on *BSD and Solaris
 	if !supportsCreateWithStickyBit && perm&ModeSticky != 0 {
-		setStickyBit(name)
+		e = setStickyBit(name)
+
+		if e != nil {
+			Remove(name)
+			return e
+		}
 	}
 
 	return nil