dsdb-show_deleted: Check if the base DN is deleted before doing a full search

dsdb-show_deleted: Check if the base DN is deleted before doing a full search

This avoids doing more work than we need to, such as a full database
scan, if the base DN is deleted.  The tdb layer cannot handle this
because we do not know to check for the isDeleted attribute there.

This was inspired by an investigation of the samr.large-dc test, which
is slow in part because of attempted SD propegation on the deleted DNs.

The samba3sam code is not compatible with this change (which implies
having checkBaseOnSearch: TRUE set on @OPTIONS), so this module is now
replaced with show_deleted_dummy for this test.

Signed-off-by: Andrew Bartlett <abartlet@samba.org>