Test correct instrumentation when a new instance is created via OkHtt…

[stannnous]

…pClient.newBuilder()

See https://github.com/raskasa/metrics-okhttp/issues/51#issuecomment-342531286

[raskasa]

Thanks. Can you refactor that testing of the new builder out into a separate unit test? I'd like to have each unit test focus on a specific thing.

Also, rebase your changes off of master to get the changes I made to fix the Travis build error.