Fix SAP systems policy receiving an empty list of instances

[dottorblaster]

Description

Fix SAP systems policy receiving an empty list of instances and marking that as not valid, thus making impossible in some cases to deregister an existing system.

How was this tested?

Existing unit tests passing, added a unit test to make sure this doesn't incur again

[nelsonkopliku]

Thanks for this @dottorblaster.

The change was introduced here https://github.com/trento-project/web/pull/2214/files, along with other required: true.

I am not sure if any other of those would cause issues.

[nelsonkopliku]

@dottorblaster, if you don't mind, may I just ask to fix this typo making the CI red, please? https://github.com/trento-project/web/actions/runs/9413405002/job/25930084979?pr=2677

[dottorblaster]

@nelsonkopliku YES

[nelsonkopliku]

thanks @dottorblaster, LGTM.

As long as @abravosuse's test is successful and @CDimonaco is fine with this, let's ship it.

[arbulu89]

@dottorblaster Thank you.
This fix means that our e2e tests are "half" complete, because we were testing this feature, but in a different case.
@abravosuse had this issue because when he "deregisters" a SAP instance, he doesn't really clean the env, he just stops the instance, so the profile file is still there.

Our e2e tests check that the cleanup button is there when there is a complete removal of the SAP instance in the agent host, which causes a different payload.

I don't know if we should update the e2e tests, as you added this UT test here, but we have this gap there...