openat/openat02.c: add a new case to test flags

create a new case to test flags for openat(2):
O_APPEND
O_CLOEXEC
O_LARGEFILE
O_NOATIME
O_NOFOLLOW
O_TRUNC

Signed-off-by: Xing Gu <gux.fnst@cn.fujitsu.com>
Signed-off-by: Cyril Hrubis <chrubis@suse.cz>