renovate.sh ignores real failures in generate-libraries.sh

[coryan]

We use renovate.sh to update the googleapis SHA. It automatically updates the generated code too:

google-cloud-cpp/external/googleapis/renovate.sh

Lines 72 to 75 in 682e065

	banner "Regenerating libraries"
	# generate-libraries fails if it creates a diff, so ignore its status.
	TRIGGER_TYPE='pr' ci/cloudbuild/build.sh \
	--docker --trigger=generate-libraries-pr || true

The || true is needed because generate-libraries.sh is intended as a CI script. It is supposed to fail if the code does not match what would happen if we generated the code, and in this case we always generate new code.

It seems we need a way to tell generate-libraries.sh to expect code diffs. Or maybe we should refactor the code such that both renovate.sh and generate-libraries.sh call some shell functions.

[dbolduc]

I don't love this, but we could run ci/cloudbuild/build.sh -t generate-libraries-pr a second time before exiting the script.