Honor connection pooling while tracing (#7979)

This PR fixes relying on r.Context().Done()
by setting

```
Connection: "close"
```

HTTP Header, this has detrimental issues for
client side connection pooling. Since this
header explicitly tells clients to turn-off
connection pooling. This causing pro-active
connections to be closed leaving many conn's
in TIME_WAIT state. This can be observed with
`mc admin trace -a` when running distributed
setup.

This PR also fixes tracing filtering issue
when bucket names have `minio` as prefixes,
trace was erroneously ignoring them.

cmd/peer-rest-client.go

@@ -499,10 +499,12 @@ func (client *peerRESTClient) doTrace(traceCh chan interface{}, doneCh chan stru
 		if err = dec.Decode(&info); err != nil {
 			return
 		}
-		select {
-		case traceCh <- info:
-		default:
-			// Do not block on slow receivers.
+		if len(info.NodeName) > 0 {
+			select {
+			case traceCh <- info:
+			default:
+				// Do not block on slow receivers.
+			}
 		}
 	}
 }