Fix the Bernoulli distribution sampler (#26864)
Summary:
The current Bernoulli distribution sampler is slightly off in that it returns true slightly too often. This is most obvious at very low p values, like p = 0, although it theoretically occurs at every probability. See https://github.com/pytorch/pytorch/issues/26807.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26864
Differential Revision: D17610459
Pulled By: ezyang
fbshipit-source-id: 28215ff820a6046822513f284793e7b850d38438
