s3: smbtorture3: Add POSIX-MKDIR test for posix_mkdir case sensitive bug.

s3: smbtorture3: Add POSIX-MKDIR test for posix_mkdir case sensitive bug.

Test does:

mkdir POSIX_foo
mkdir POSIX_Foo
mkdir POSIX_foo/Foo
mkdir POSIX_foo/foo
mkdir POSIX_Foo/Foo
mkdir POSIX_Foo/foo

Which should pass a SMB1 POSIX extensions server
as posix mkdir should always be case sensitive
no matter what the share is set to.

Mark as knownfail for now.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13803

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>
(cherry picked from commit f0decb31fff24ceb57d23bebbfb87aa0e5103947)