Add TIMEOUT as an error

Change-Id: If6807fed03fd57821c82d9cad7d9efe905a01108
diff --git a/mininet-test.rules b/mininet-test.rules
index d442326..1130c2d 100644
--- a/mininet-test.rules
+++ b/mininet-test.rules
@@ -3,8 +3,10 @@
 # Rules are in priority order - first matching rule
 # triggers and the rest are ignored.
 
-# Failed full tests will be marked with FAILED
+# Failed full tests will be marked with FAILED,
+# and a pexpect TIMEOUT is also almost certainly an error
 error /FAILED/
+error /TIMEOUT/
 
 # Warn on exceptions and sub-errors
 warn /(?i)^exception/