[CI] Updated test to use revision tag when revision is present or else use nightly

What does this MR do?

Fetching the revision tag and storing it in the variables file.

Using the revision as tag if revision is present or else using nightly tag

This MR would potentially fix the random failures due to version mismatch between the app and the qa test image.

Related issues

gitlab-org/quality/quality-engineering/team-tasks#1562 (closed)

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened
• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.