[mongo] refactor mongo check into mongo_instance class

[lu-zhengda]

What does this PR do?

Motivation

Additional Notes

Review checklist (to be filled by reviewers)

• [ ] Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• [ ] Changelog entries must be created for modifications to shipped code
• [ ] Add the qa/skip-qa label if the PR doesn't need to be tested during QA.
• [ ] If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 95.44419% with 20 lines in your changes missing coverage. Please review.

Project coverage is 89.55%. Comparing base (c5e3a19) to head (b146cff). Report is 24 commits behind head on master.

Additional details and impacted files

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