ipa-kdb: Fix legacy password hashes generation
    
    We were not searching for objectclass so the test to se if a user had the
    posixAccount attribute was failing and the user was not marked as ipa_user.
    This in turn caused us to not synchronize legacy hashes by not trying to store
    the userPassword attribute.
    
    Fixes: https://fedorahosted.org/freeipa/ticket/1820