[circleci] parallelize Test::Nginx suite

[mikz]

Reduces CircleCI prove from 53 to 13s.
Automatically runs prove in parallel when nproc is available. And make prove will run tests in randomized directories and ports.

To achieve this all tests need to allocate a random port to listen on. That includes the TCP/UDP servers provided by Test::Nginx to stub DNS server.

The environment configuration can now configure echo/management/backend ports:

return {
  port = {
      apicast = '8080',
      management = '8090',
      backend = '8081',
      echo = '8081',
    },
}

[davidor]

So maybe we should wait until we solve the problem before merging this, right?

[mikz]

Sure, this can't be merged right now.

[davidor]

Great! 👍