Fix stream tests to work with wonko-client 0.1.4
Fix stream tests to work with wonko-client 0.1.4

- Since execution in wonko-client is async, we can not rely on the
  messages to be sent serially anymore. This test attested on the first
  of the events received, which is necessarily the first event sent to
  kafka, but not necessarily the first event sent to wonko-client.

staples-sparx/Wonko