[Flakey Tests] TestAsyncTableGetMultiThreaded

I've already cut down the number of threads used by this test but it failed in nightly last night unable to close out its xml and locally it failed too in a run overnight. I ran it under harness and it seems well-behaved. It doesn't use much memory – 700MB – and thread counts are usual (~450). It does use near 100% CPU which is a little unusual. Otherwise, looks fine.

Let me keep an eye on it. Could down the thread count more and use less processes... this makes it use less CPU. There does seems a bunch of overlap with tests done elsewhere.