don't run function test when no AK env viriable

Author: JacksonTian

.travis.yml

@@ -18,7 +18,9 @@ install:
   - pip install mock
 
 script:
-  - make test-all
+  - make lint
+  - make test
+  - '[[ $ACCESS_KEY_ID && $ACCESS_KEY_SECRET ]] && make functional-test'
 
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