s3: smbtorture: Add new SMB2-DIR-FSYNC test to show behavior of FSYNC on directories.

s3: smbtorture: Add new SMB2-DIR-FSYNC test to show behavior of FSYNC on directories.

Tests against a directory handle on the root of a share,
and a directory handle on a sub-directory in a share.

Check SEC_DIR_ADD_FILE and SEC_DIR_ADD_SUBDIR separately,
either allows flush to succeed.

Passes against Windows.

Regression test for:

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13428

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Fri May 18 02:38:50 CEST 2018 on sn-devel-144

(cherry picked from commit d42f467a25e75e5487a00378609a24809ddc83ee)