Make gateway test less racey
Make gateway test less racey

The http-gateway tests work on local systems, but tend to fail on
CI. This appeared to be due largely to a race condition between
the code that starts the server and the tests themselves.

- Add waitForHttpGatewayToBeReady()
- Pull gw.Run(done) into JustBeforeEach

[Github projectriff/riff#305]

Add 10sec timeout to waitForHttpGatewayToBeReady()

- Configure polling for 100ms

[Github #305]

Use /application/status for http-gateway liveness

markfisher/sk8s,markfisher/sk8s,markfisher/sk8s,markfisher/sk8s