Improve test coverage of capabilities

[simontesar]

Some capabilities are either uncovered or not verified. This is an non-exhaustive list, to be extended:

• power.reset: potentially verify that a reset happened, not only that the annotation was consumed by the operator
• manager.reset: potentiall verify that status.lastResetTime has advanced, not only non-null
• inventory.storages: assert storage in status
• boot.order-*: ensure that verification job is as vendor-independent as possible
• events.*: uncovered
• account.*: uncovered
• firmware.*: uncovered