Bug Description:
We should have different tiers of tests:
tier0 - basic functionality (installation, instance startup, basic operations, import/export, etc.)
tier1 - functional tests for the most used features
tier2 - functional tests for the less used features and tests that take more time to complete (stress tests)
tier3 - long duration tests.

Fix Description:
Use pytest marks per test module or individually.

Fixes https://pagure.io/389-ds-base/issue/50353

Reviewed by: spichugi (Thanks!)