Fix ASSERT failure and re-enable setnumcapabilities001
The assertion failure was fairly benign, I think, but this fixes it. I've been running the test repeatedly for the last 30 mins and it hasn't triggered. There are other problems exposed by this test (see #12038), but I've worked around those in the test itself for now. I also copied the relevant bits of the parallel library here so that we don't need parallel for the test to run.
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