Report keyboard interrupt as abnormal (infra) failure

R=tandrii@chromium.org
BUG=579589

Review-Url: https://codereview.chromium.org/2125713002
diff --git a/presubmit_support.py b/presubmit_support.py
index 4f72d5c..4a388ca 100755
--- a/presubmit_support.py
+++ b/presubmit_support.py
@@ -1829,4 +1829,4 @@
     sys.exit(main())
   except KeyboardInterrupt:
     sys.stderr.write('interrupted\n')
-    sys.exit(1)
+    sys.exit(2)