Fixes #1261 - Intermittent H2C test failure AsyncIOServletTest.testAsyncReadEarlyEOF.

Delayed abrupt output shutdown in case of HTTP/2, to allow to reply to
SETTINGS frames exchanged during the preface.

tests/test-http-client-transport/src/test/java/org/eclipse/jetty/http/client/AsyncIOServletTest.java

@@ -1024,6 +1024,10 @@ public class AsyncIOServletTest extends AbstractTest
                 break;
             case H2C:
             case H2:
+                // In case of HTTP/2, we not only send the request, but also the preface and
+                // SETTINGS frames. SETTINGS frame need to be replied, so we want to wait to
+                // write the reply before shutting output down, so that the test does not fail.
+                Thread.sleep(1000);
                 Session session = ((HttpConnectionOverHTTP2)connection).getSession();
                 ((HTTP2Session)session).getEndPoint().shutdownOutput();
                 break;