improve some reporting for fakelowp tests (#38428)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38428
use and log a randomly generated seed with each test
Test Plan: locally tested
Reviewed By: amylittleyang
Differential Revision: D21554466
fbshipit-source-id: 008185d13116ec8553b082150a355ba87682bf6a
