Don't use output argument for CalledProcessError (Python 2.7 only)

cros_mark_as_stable.py

Index: cros_mark_as_stable.py
diff --git a/cros_mark_as_stable.py b/cros_mark_as_stable.py
index b2f2cd4067600aa7c275427dfd9a466def960752..5df6a83fef1989d811fe28c895ae6d228387185f 100755
--- a/cros_mark_as_stable.py
+++ b/cros_mark_as_stable.py
@@ -248,7 +248,8 @@ def _SimpleRunCommand(command):
   stdout = proc_handle.communicate()[0]
   retcode = proc_handle.wait()
   if retcode != 0:
-    raise subprocess.CalledProcessError(retcode, command, output=stdout)
+    _Print(stdout)
+    raise subprocess.CalledProcessError(retcode, command)
   return stdout