smoke: Fix smoke test issue due to EC API change

[ericywl]

The EC API that we use to get available stack versions was recently changed to remove previously release SNAPSHOTs. This causes some OS smoke tests to fail since we use SNAPSHOTs for all of the tests and some of them are missing. This PR fixes the issue by falling back to released versions instead of SNAPSHOTs if they are not available.

[github-actions]

🤖 GitHub comments

Just comment with:

• run docs-build : Re-trigger the docs validation. (use unformatted text in the comment!)

[mergify]

This pull request does not have a backport label. Could you fix it @ericywl? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-7.17 is the label to automatically backport to the 7.17 branch.
• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit.
• backport-9./d is the label to automatically backport to the 9./d branch. /d is the digit.
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-8 is the label that automatically backports to all active minor branches for the 8 major.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.

[elasticmachine]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: af9ceaf

Failed CI Steps

• Package x86_64

cc @ericywl

[endorama]

Do we plan to use this terraform code again? If not, shouldn't we remove it?

Suggested change

# local REGION=$(echo var.region | terraform console | tr -d '"')

The terraform code we are initializing here could be removed (at least partially)?