[TEST] Change es.node.mode default for tests to `local`

In order to speed up test execution we should run in local mode by
default. CI builds will still use network builds all the time.
I was actually laughing at people in the past doing this. But I got really convinced by a huge mistake I made lately and @mikemccand who also uses this pattern since it's much harder to overlook that a `!` so in theory I agree. What about adding `String#isEmpty()` that is the negation of `hasLength` instead?