IPA: do not add domain name unconditionally
    
    Depending on the server-side configuration the extdom plugin can return
    short or fully qualified names for IPA objects. The client must handle
    the names according to its own configuration and not add the domain part
    of the fully-qualified name unconditionally.
    
    Resolves https://fedorahosted.org/sssd/ticket/2647
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>