Add timeout to suppression list for http_shutdown_test

tests/standalone/standalone.status

 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 package/invalid_uri_test: Fail, OK # Fails intentionally
 
 [ $runtime == vm && $checked ]
 # These tests have type errors on purpose.
 io/process_invalid_arguments_test: Fail, OK
 io/directory_invalid_arguments_test: Fail, OK
@@ skipping 24 matching lines @@
 io/directory_non_ascii_test: Pass, Fail
 io/process_non_ascii_test: Pass, Fail
 
 [ $runtime == vm && $system == windows ]
 io/file_system_links_test: Skip  # No links on Windows.
 io/test_extension_fail_test: Fail  # Issue 7157
 io/secure_server_stream_test: Pass, Crash, Timeout  # Issue 6893
 io/secure_server_test: Pass, Crash, Fail, Timeout  # Issue 6893
 io/secure_no_builtin_roots_test: Pass, Crash  # Issue 7157
 io/secure_socket_bad_certificate_test: Pass, Crash, Fail, Timeout  # Issue 7157
-io/http_shutdown_test: Pass, Fail  # Issue 7294
+io/http_shutdown_test: Pass, Fail, Timeout  # Issue 7294
 
 [ $compiler == none && $runtime == drt ]
 io/*: Skip # Don't run tests using dart:io in the browser
 crypto/*: Skip # Don't run tests using dart:io in the browser
 package/*: Skip # Do not run those in Dartium.
 
 [ $compiler == dartc ]
 *: Skip
 
 [ $compiler == frog ]
@@ skipping 30 matching lines @@
 [ $compiler == dart2js && $browser ]
 *: Skip
 
 [ $compiler == dart2js && $checked ]
 io/http_read_test: Skip # Timeout TODO(ngeoffray): investigate
 io/list_input_stream_test: Skip # Timeout TODO(ngeoffray): investigate
 
 [ $compiler == dart2dart ]
 # Skip until we stabilize language tests.
 *: Skip