CVE-2018-10919 tests: Add extra test for dirsync deleted object corner-case

CVE-2018-10919 tests: Add extra test for dirsync deleted object corner-case

The acl_read.c code contains a special case to allow dirsync to
work-around having insufficient access rights. We had a concern that
the dirsync module could leak sensitive information for deleted objects.
This patch adds a test-case to prove whether or not this is happening.

The new test case is similar to the existing dirsync test except:
- We make the confidential attribute also preserve-on-delete, so it
  hangs around for deleted objcts. Because the attributes now persist
  across test case runs, I've used a different attribute to normal.
  (Technically, the dirsync search expressions are now specific enough
  that the regular attribute could be used, but it would make things
  quite fragile if someone tried to add a new test case).
- To handle searching for deleted objects, the search expressions are
  now more complicated. Currently dirsync adds an extra-filter to the
  '!' searches to exclude deleted objects, i.e. samaccountname matches
  the test-objects AND the object is not deleted. We now extend this to
  include deleted objects with lastKnownParent equal to the test OU.
  The search expression matches either case so that we can use the same
  expression throughout the test (regardless of whether the object is
  deleted yet or not).

This test proves that the dirsync corner-case does not actually leak
sensitive information on Samba. This is due to a bug in the dirsync
code - when the buggy line is removed, this new test promptly fails.
Test also passes against Windows.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13434

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>