Brain test for eirini persi

[viovanov]

Acceptance Criteria

• [ ] brain test that runs when eirini is enabled
• [ ] should verify that a persi service instance can be created
• [ ] should verify that an app can store data, be restarted and data is preserved
• [ ] should verify that multiple app instances can write to the same persistent volume

[mudler]

As a side note, there is already a fixture available here: https://github.com/SUSE/catapult/tree/v2-experiment/contrib/samples/eirini-persi-test

[fargozhu]

add checkboxes to the acceptance criteria so we know what remains from this issue.