Add aesce test string filter

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/.travis.yml b/.travis.yml
index 75f4c64..3a608f5 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -150,7 +150,7 @@
         - scripts/config.py set MBEDTLS_AES_USE_HARDWARE_ONLY
         - make generated_files
         - make
-        - programs/test/selftest
+        - programs/test/selftest aes | grep "using AESCE"
         - tests/context-info.sh
 
 after_failure: