use parsers build config in e2e tests

[davidstanke]

There's a build config specifically for the parsers (bq-workers/parsers.cloudbuild.yaml), which the terraform installer instructions reference. But the e2e test doesn't use this; it just build the containers directly.

Let's rework the e2e config so it uses parsers.cloudbuild.yaml, in order to ensure that the parser builder config stays functional.