Report keyboard interrupt as abnormal (infra) failure

R=tandrii@chromium.org
BUG=579589

Review-Url: https://codereview.chromium.org/2125713002

presubmit_support.py

@@ -1829,4 +1829,4 @@ if __name__ == '__main__':
     sys.exit(main())
   except KeyboardInterrupt:
     sys.stderr.write('interrupted\n')
-    sys.exit(1)
+    sys.exit(2)