toolchain-utils: Launch tryjobs from chroot.

This is to workaround a bug in launching tryjobs from
outside chroot.

BUG=None
TEST=can launch tryjobs

Change-Id: Ie0d48e9f8f487ef9a9eeebd627948492f65fed31
Reviewed-on: https://chromium-review.googlesource.com/c/1490571
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>
Commit-Queue: Manoj Gupta <manojgupta@chromium.org>
Tested-by: Manoj Gupta <manojgupta@chromium.org>
diff --git a/cros_utils/buildbot_utils.py b/cros_utils/buildbot_utils.py
index 0d93765..d1080e0 100644
--- a/cros_utils/buildbot_utils.py
+++ b/cros_utils/buildbot_utils.py
@@ -1,3 +1,4 @@
+# -*- coding: utf-8 -*-
 # Copyright 2017 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
@@ -114,7 +115,7 @@
 
   # Launch buildbot with appropriate flags.
   build = buildbot_name
-  command = ('cros tryjob --yes --json --nochromesdk  %s %s %s' %
+  command = ('cros_sdk -- cros tryjob --yes --json --nochromesdk  %s %s %s' %
              (tryjob_flags, patch_arg, build))
   print('CMD: %s' % command)
   _, out, _ = RunCommandInPath(chromeos_root, command)