[cryptohome] make guest-mode homedir mount with -rwx------

BUG=chromium-os:13173
TEST=unit tests, manual: ls -ald /home/chronos/user -> drwx------ 10 chronos chronos 500 Apr 21 14:26 /home/chronos/user/

Change-Id: Ifd60b6c31e773d55d334a6f6c58565c2c64365b8

R=jimhebert@chromium.org

Review URL: http://codereview.chromium.org/6895001
1 file changed