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* Change parameterized testing system to be compatible with unittest

Summary: The previous implementation of parameterized testing worked by modifying test.common_utils inplace.  This doesn't work in general because unittest's contract with test modules is such that it must be able to load the module and run the test itself.  Because the previous implementation needed to load the module and modify it, it is incompatible.

Reviewed By: mthrok

Differential Revision: D21964676
Co-authored-by: Ben Mehne <bmehne@fb.com>