Running Docker on the host network is not supported on GCB, which is breaking our builds over at getsentry/sentry. This patch removes the use of sentry-cli and does a manual `curl` request to create the test event.
This is a long-needed test that tests the whole pipeline from Nginx, Relay, to Kafka, and Snuba. The final missing piece is testing the Symbolicator integration.
This PR is also a follow up to #576 as it didn't solve the Relay issues fully (the earlier fix was a coincidence or is not as reliable as it seemed).
Fixes#486 (finally?).
