atc: structure: only assert on pipeline IDs
atc: structure: only assert on pipeline IDs

concourse/concourse#5314

This _should_ result in more robust tests -- the important assertion in
each of these cases seemed to be simply about the set of pipelines that
were visible, and the exact JSON content was a bit of a detail.

Now it should be possible to freely change the JSON structure of those
endpoints without breaking the tests (as long as the "id" field keeps
the same behaviour).

Signed-off-by: Jamie Klassen <d740210502544aa0776b92978c6db85774130b86@pivotal.io>
Co-authored-by: Bishoy Youssef <9b4d1ba1708a9b42aa1e22343aa1f23ecf97ab43@pivotal.io>

concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse