[v22.3.x] test: memory leak in test_cluster_rpunit

[vbotbuildovich]

Backport #3338 to branch v22.3.x

[andrewhsu]

@dotnwat i think i saw this issue in a vtools v22.3.x PR: https://buildkite.com/redpanda/vtools/builds/5518#0185f430-0ccc-430d-8d20-eaf2166827df/6-4808

so i kicked off a backport to v22.3.x and it cherry-picked clean: #8471

but feel free to close without merge if you don't think the backport will address what i saw.

[dotnwat]

@andrewhsu unfortunately that error you saw looks like it is a different issue. i don't see any reason for not backporting the lsan fix like you did, but could you turn the failure you saw into a ci-failure ticket?

[r-vasquez]

@dotnwat, @andrewhsu I opened: #8508 because I saw a similar failure (details in the ticket).