MAGETWO-53689: Integration tests on Travis CI are very close to exceed time limit

- splitting into 3 sets

.travis.yml

@@ -19,6 +19,7 @@ env:
     - TEST_SUITE=unit
     - TEST_SUITE=integration INTEGRATION_INDEX=1
     - TEST_SUITE=integration INTEGRATION_INDEX=2
+    - TEST_SUITE=integration INTEGRATION_INDEX=3
     - TEST_SUITE=static
 cache:
   apt: true