Use FAIL to catch specific FAIL:  messages.

Change-Id: I406b53a499a34fb661a892ce46a232ea3e5e0138
diff --git a/mininet-test.rules b/mininet-test.rules
index 1130c2d..c713ecf 100644
--- a/mininet-test.rules
+++ b/mininet-test.rules
@@ -5,7 +5,7 @@
 
 # Failed full tests will be marked with FAILED,
 # and a pexpect TIMEOUT is also almost certainly an error
-error /FAILED/
+error /FAIL/
 error /TIMEOUT/
 
 # Warn on exceptions and sub-errors