Add test coverage to collectors

[jpellizzari]

We need automated test coverage on:

• pkg/collector
• pkg/rolecollector
• pkg/objectscollector

[jpellizzari]

cc @squaremo If you can post your multi-cluster envtest stuff that would be awesome!

[squaremo]

This is what I've done for a similar testing requirement: https://github.com/weaveworks-experiments/fleeet/blob/main/module/controllers/remote_test.go#L137
It's not horrendously expensive, but it does run >1 etcd; I think in theory it's possible to multiplex onto a single etcd, but I balked at trying that.

[enekofb]

See for example an integration test for collector in another PR

It would be useful to consider it in this ticket

[jpellizzari]

We have a larger suite built out now that hit major parts of the collector. Closing.