smbd: unix_convert: Ensure we don't call get_real_filename on POSIX paths.

smbd: unix_convert: Ensure we don't call get_real_filename on POSIX paths.

For posix_pathnames don't blunder into the name_has_wildcard OR
get_real_filename() codepaths as they may be doing case insensitive lookups.
So when creating a new POSIX directory 'Foo' they might
match on name 'foo'.

Remove POSIX-MKDIR from knownfail.

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>
Autobuild-User(master): Volker Lendecke <vl@samba.org>
Autobuild-Date(master): Sun Feb 24 14:04:14 CET 2019 on sn-devel-144

(cherry picked from commit 12da33e2bbce657f25abe9bc4cb936ca4615b30f)