Fix scenario import and add test UUIDs
The scenario manager module referenced tempest.scenario.manager without importing it, causing AttributeError when check-uuid scanned test classes. An unused tempest.test import was also present.
This change adds the missing import, removes the unused import, and creates a uuidgen testenv. Running check-uuid after the fix generated idempotent_id decorators for 30 test methods across 8 API test modules.
Check-uuid command comes from tempest package, available in requirements.txt, hence added to tox.ini file to install tempest.
Assisted-By: Claude Sonnet 4.5 Change-Id: I81f6a4e37ac4549dde48034e0c3e819561b501ff Signed-off-by: Chandan Kumar (raukadah) chkumar@redhat.com