lib: tst_path_has_mnt_flags: Add NULL path as tmpdir

Change the tst_path_has_mnt_flags() to use tst_tmpdir if path is NULL.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
open/open12.c: add new tests

Add new tests for open(2)
O_APPEND
O_NOATIME
O_CLOEXEC
O_LARGEFILE

Signed-off-by: Zeng Linggang <zenglg.jy@cn.fujitsu.com>
Signed-off-by: Cyril Hrubis <chrubis@suse.cz>