On shutdown Pingora always sleep for `graceful_shutdown_timeout_seconds`

Describe the bug

On shutdown Pingora always sleep for graceful_shutdown_timeout_seconds, regardless how quick all the tokio had runtimes finished. Problematic code is here:

pingora/pingora-core/src/server/mod.rs

Lines 575 to 585 in a6dbd1a

    
           let shutdowns: Vec<_> = runtimes 
        
               .into_iter() 
        
               .map(|(rt, name)| { 
        
                   info!("Waiting for runtimes to exit!"); 
        
                   let join = thread::spawn(move || { 
        
                       rt.shutdown_timeout(shutdown_timeout); 
        
                       thread::sleep(shutdown_timeout) 
        
                   }); 
        
                   (join, name) 
        
               }) 
        
               .collect();

Pingora correctly waits for runtime to shutdown, but then for some reason adds thread::sleep for the same amount which doesn't make any sense I think.

Pingora info

Please include the following information about your environment:

Pingora version: Master
Rust version: doesn't matter
Operating system version: doesn't matter

Steps to reproduce

Do a Pingora reload and set graceful_shutdown_timeout_seconds to 10 minutes, even empty without any services old server will die exactly after that amount of time.

Expected results

As it's a timeout, I was expecting Pingora to stop as soon as all runtimes has finished.

	let shutdowns: Vec<_> = runtimes
	.into_iter()
	.map(\|(rt, name)\| {
	info!("Waiting for runtimes to exit!");
	let join = thread::spawn(move \|\| {
	rt.shutdown_timeout(shutdown_timeout);
	thread::sleep(shutdown_timeout)
	});
	(join, name)
	})
	.collect();