fix: remove EXIT trap from wait_for_available_zone.sh

[sudheer-quad]

This PR removes an EXIT trap from a sourced script that was unintentionally overriding the parent shell's trap, causing resource leaks.
Source

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a resource management issue where a sourced script was unintentionally interfering with the parent shell's trap settings. By removing the global EXIT trap and implementing explicit cleanup of temporary files, the script now avoids potential side effects on the parent environment while maintaining resource hygiene.

Highlights

• Trap Removal: Removed the global EXIT trap from the script to prevent it from overriding the parent shell's trap configuration.
• Manual Cleanup: Added explicit removal of temporary files before script exit to ensure proper resource cleanup without relying on the trap.

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[gemini-code-assist]

Code Review

This pull request modifies the wait_for_available_zone.sh script to remove the EXIT trap and manually clean up temporary files upon fatal errors and normal completion. The review feedback points out two main issues when the script is sourced by a parent shell: first, calling exit 1 will terminate the parent shell session, which can be prevented by checking if the script is sourced and using return instead; second, the script's internal toggling of errexit will permanently alter the parent shell's settings, so the original state should be saved and restored.

[gemini-code-assist]

Since this script is sourced by a parent shell, calling exit 1 will terminate the entire parent shell session (such as an interactive terminal or a parent script). To prevent this while still allowing the script to be executed directly, check if the script is being sourced or executed, and use return or exit accordingly.

Suggested change

	rm -f "$ZONE_EXPORT" "$ZONE_OUTPUT"
	exit 1
	rm -f "$ZONE_EXPORT" "$ZONE_OUTPUT"
	if [[ "${BASH_SOURCE[0]}" != "${0}" ]]; then
	return 1
	else
	exit 1
	fi

[gemini-code-assist]

Sourcing this script will permanently alter the parent shell's errexit (set -e) setting because of the set +e and set -e calls inside the loop (lines 25 and 34). If the parent shell had set -e disabled, it will end up with set -e enabled after sourcing this script.

To prevent this side-effect, consider saving the original state of errexit at the beginning of the script and restoring it at the end:

# At the beginning of the script
OLD_ERREXIT=$(shopt -po errexit)

# At the end of the script (and before any exit/return)
eval "$OLD_ERREXIT"