user, migration: use LDAPClient for ad-hoc LDAP connections
    
    Use LDAPClient instead of ldap2 for ad-hoc remote LDAP connections in the
    user_status and migrate-ds plugins.
    
    Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>