fix(ci): reorder gke tags and labels variable expansions

[BradLugo]

Description

If you're really unlucky, you can get a . at the end of the tags variable, which will be substituted for - after we replace the last - with x. GKE doesn't allow for - at the end of the string, which is why we change the last -.

See openshift/release#47789 for a real-world example of this problem.

These changes reorders the shell expansion so we first replace all . with -, then delete the last -.

Cherry-picked from #1513

Testing Performed

Testing the variable expansions:

# Before
❯ JOB_NAME=rehearse-47789-pull-ci-stackrox-scanner-release-2.32-e2e-tests
❯ tags="stackrox-ci"
❯ tags="${tags},stackrox-ci-${JOB_NAME:0:50}"
❯ echo "${tags}"
stackrox-ci,stackrox-ci-rehearse-47789-pull-ci-stackrox-scanner-release-2.
❯ tags="${tags/%-/x}"
❯ echo "${tags}"
stackrox-ci,stackrox-ci-rehearse-47789-pull-ci-stackrox-scanner-release-2.
❯ tags="${tags//./-}"
❯ echo "${tags}"
stackrox-ci,stackrox-ci-rehearse-47789-pull-ci-stackrox-scanner-release-2-

# After
❯ JOB_NAME=rehearse-47789-pull-ci-stackrox-scanner-release-2.32-e2e-tests
❯ tags="stackrox-ci"
❯ tags="${tags},stackrox-ci-${JOB_NAME:0:50}"
❯ tags="${tags//./-}"
❯ tags="${tags/%-/}"
❯ echo "${tags}"
stackrox-ci,stackrox-ci-rehearse-47789-pull-ci-stackrox-scanner-release-2

[openshift-ci]

@BradLugo: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/e2e-tests	1df1326	link	false	/test e2e-tests
ci/prow/store-genesis-dump	1df1326	link	false	/test store-genesis-dump
ci/prow/store-db-dump	1df1326	link	false	/test store-db-dump
ci/prow/push-images	1df1326	link	true	/test push-images
ci/prow/slim-e2e-tests	1df1326	link	false	/test slim-e2e-tests
ci/prow/images	1df1326	link	true	/test images
ci/prow/style-checks	1df1326	link	true	/test style-checks

Full PR test history. Your PR dashboard.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository. I understand the commands that are listed here.