Fix LDAPCreate search failure
    
    LDAPCreate reports "search criteria was not specific enough" when LDAP
    object created in LDAPCreate shares its container with other LDAP objects
    and there is one with the same name and RDN attribute.
    
    Pass objectclass to find_entry_by_attr() function used to retrieve
    newly created object for POST_CALLBACK to identify correct LDAP
    object.
    
    https://fedorahosted.org/freeipa/ticket/1864