Move STEP_WARNINGS and STEP_FAILURE into constants.py.

BUG=none
TEST=remote trybot, unit tests.

Change-Id: I819c7e7b4e2f85aaf95dc5cc03adab6bdd541bb7
Reviewed-on: https://gerrit.chromium.org/gerrit/25500
Reviewed-by: Brian Harring <ferringb@chromium.org>
Commit-Ready: David James <davidjames@chromium.org>
Tested-by: David James <davidjames@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index 9533867..e38f668 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -373,8 +373,7 @@
         success = results_lib.Results.BuildSucceededSoFar()
         if exception_thrown and success:
           success = False
-          print >> sys.stderr, """
-@@@STEP_FAILURE@@@
+          print >> sys.stderr, "\n" + constants.STEP_WARNINGS + """
 Exception thrown, but all stages marked successful. This is an internal error,
 because the stage that threw the exception should be marked as failing."""