Add debug info for prow script

[evankanderson]

We're seeing errors like https://storage.googleapis.com/knative-prow/logs/continuous_net-gateway-api_main_periodic/1546926961899606016/build-log.txt

I suspect something related to #315 (possibly that services are being set as NodePort on GKE), but I'd like to see the commands used to set up the cluster to verify.

[codecov]

Codecov Report

Merging #332 (5bb4ce3) into main (07b7020) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #332   +/-   ##
=======================================
  Coverage   16.55%   16.55%           
=======================================
  Files          21       21           
  Lines        3172     3172           
=======================================
  Hits          525      525           
  Misses       2616     2616           
  Partials       31       31           

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[carlisia]

/lgtm
/approve

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: carlisia, evankanderson

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