Docker exec example with output

[Steven Miller]

    let config = CreateExecOptions {
        cmd: Some(vec!["echo", "hello"]),
        attach_stdout: Some(true),
        ..Default::default()
    };

    let exec = docker.create_exec(&container.id, config).await?;
    let start_exec_options = Some(StartExecOptions {
        detach: false,
        ..StartExecOptions::default()
    });
    let log_output = docker.start_exec(&exec.id, start_exec_options);
    let mut start_exec_result = log_output.await?;

    match start_exec_result {
        StartExecResults::Attached { output, .. } => {
            let mut output = output
                .map(|result| {
                    match result {
                        Ok(log_output) => println!("{}", log_output.to_string()),
                        Err(error) => eprintln!("Error while reading log output: {}", error),
                    }
                })
                .fuse();

            // Run the output stream to completion.
            while output.next().await.is_some() {}
        },
        StartExecResults::Detached => {
            println!("Exec started in detached mode");
        }
    }