WIP: Testing: discovery: check number of goroutines

[dgrisonnet]

What this PR does / why we need it:

How does this change affect the cardinality of KSM: (increases, decreases or does not change cardinality)

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

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[rexagod]

We may want to incorporate https://github.com/uber-go/goleak as well, WDYT?

[dgrisonnet]

Yes that would definitely be a great addition, but I didn't have time to modify our integration that. I just want to check if #2478 can cause a goroutine explosion.