optimize listing operation concurrency (#12728)

- remove use of getOnlineDisks() instead rely on fallbackDisks()
  when disk return errors like diskNotFound, unformattedDisk
  use other fallback disks to list from, instead of paying the
  price for checking getOnlineDisks()

- optimize getDiskID() further to avoid large write locks when
  looking formatLastCheck time window

This new change allows for a more relaxed fallback for listing
allowing for more tolerance and also eventually gain more
consistency in results even if using '3' disks by default.

cmd/utils.go

@@ -513,6 +513,7 @@ func newCustomHTTPProxyTransport(tlsConfig *tls.Config, dialTimeout time.Duratio
 		Proxy:                 http.ProxyFromEnvironment,
 		DialContext:           xhttp.DialContextWithDNSCache(globalDNSCache, xhttp.NewInternodeDialContext(dialTimeout)),
 		MaxIdleConnsPerHost:   1024,
+		MaxConnsPerHost:       1024,
 		WriteBufferSize:       16 << 10, // 16KiB moving up from 4KiB default
 		ReadBufferSize:        16 << 10, // 16KiB moving up from 4KiB default
 		IdleConnTimeout:       15 * time.Second,