Fix merge train trainsient test flakiness

What does this MR do?

I did a little bit of clean up and refactor but the main purpose of this MR is to:

• Change pipeline status expectation to just "passed" since the full text is different at times #324357 (comment 528269699).
• Move pipeline status expectation to a more appropriate state of the process.

To remedy this flakiness #324357 (closed)

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Related to #324357 (closed)