Bigtable system test has a "race condition" if run simultaneously on same project

Two builds (1682 and 1683) were happening simultaneously and this caused a Bigtable system test check to fail in the second build (1683)

>       self.assertEqual(len(instances), len(EXISTING_INSTANCES) + 1)
E       AssertionError: 2 != 3

This is because EXISTING_INSTANCES is set at module setup time while the test case is run later.

I'm not sure what a realistic fix should be?

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