engine: Propagate error message when querying for LDAP users

A previous commit fixed this issue for users/groups(dcfd219).
call setHandleFailure(true) on users as well so the handleQueryError
code will be called on ldap provider errors.

Change-Id: I9362e48a36be61fd75c386883b9ccaf28ed15a27
Signed-off-by: Mooli Tayer <mtayer@redhat.com>