Investigate issue #4461 (#4521)

* Code to investigate issue #4461 (rare test failure in TestListenAndServeTLS)

* Use UTCNow() instead of time.Now().UTC()

cmd/server-mux_test.go

@@ -390,11 +390,17 @@ func TestServerListenAndServeTLS(t *testing.T) {
 			Transport: tr,
 		}
 		// Keep trying the server until it's accepting connections
+		start := UTCNow()
 		for {
 			res, _ := client.Get("https://" + addr)
 			if res != nil && res.StatusCode == http.StatusOK {
 				break
 			}
+			// Explicit check to terminate loop after 5 minutes
+			// (for investigational purpose of issue #4461)
+			if UTCNow().Sub(start) >= 5*time.Minute {
+				t.Fatalf("Failed to establish connection after 5 minutes")
+			}
 		}
 
 		// Once a request succeeds, subsequent requests should