Util Sockets: Tidy up connect() handling
    
    The connect() man page says waiting on a non-blocking connect should be done
    by checking for writability, so drop checking for readability. Also check
    for EALREADY as an acceptable error to retry on.
    
    Related:
    https://fedorahosted.org/sssd/ticket/2968
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>