Test fork fix

[gnossen]

An attempt to test out https://github.com/grpc/grpc/pull/30473

[drfloob]

I ran Basic Tests Python Linux 5 times and all succeeded. I don't know of a great way to run this particular set of tests in large number, nor exactly how flaky this was beforehand to see if 5 is significant. @gnossen this seems promising, we should follow up with the beam folk to see if this solves the issue.

https://source.cloud.google.com/results/invocations/8c863d6f-1baf-47db-86bf-24940abcef83/targets https://fusion2.corp.google.com/invocations/b556c61a-062f-49bc-99e1-5170ffa8f49e/targets https://fusion2.corp.google.com/invocations/0bc44a8a-efd7-4f0f-868b-5681e180607f/targets https://fusion2.corp.google.com/invocations/2da74b06-1ea3-463e-9517-689bfd965e9d/targets https://fusion2.corp.google.com/invocations/7bc476f0-01a4-4d40-888e-4651bf3b291d/targets

[drfloob]

CC @ctiller

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