test-def: create SLO definitions in setup so SLO read ops have data

[JoshMock]

Opened from failing KB functional tests in test/functional/kb/definitions/. SLO read ops fail with 404 Not Found on the stack run because no SLO definitions exist, so get/snapshot/bulk_snapshot have no data to operate on.

Create SLO definitions in setup (or provide a fixture) and capture their ids, then reference them in the affected definitions so the read ops have data. Add teardown to remove the created SLOs.

Failing test definitions (stack):

• slo_bulk_snapshot_op.yml
• slo_get_definitions_op.yml
• slo_get_snapshot_op.yml