for my $host (...) {
    $ssh{$host} = Net::OpenSSH->new($host, ...);
    if($ssh{$host}->error) {
        print STDOUT "Still waiting for SSH. Retrying in 5 seconds...\n";
        sleep 5;
        redo;
    }
    else {
        print STDOUT "SSHD is back up. Continuing...\n";
    }
}