IPA: do not fail if view name lookup failed on older versions
    
    Depending on the version 389ds return a different error code if the
    search for the view name failed because our dereference attribute
    ipaAssignedIDView is not known. Newer version return
    LDAP_UNAVAILABLE_CRITICAL_EXTENSION(12) which is translated to
    EOPNOTSUPP and older versions return LDAP_PROTOCOL_ERROR(2) which is
    returned as EIO. In both cases we have to assume that the server is not
    view aware and keep the view name unset.
    
    Resolves https://fedorahosted.org/sssd/ticket/2650
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>