run_perf_tests: Add option to find test binary in out dir. This allows us to run the perf test runner script from any directory and use that as a basis to find the most recently modified test suite binary. This saves us from chdir()ing into test directory every time we want to run a test suite. Ideally this should move into the test utils folder to be used by the gold tests script as well. Bug: angleproject:7671 Change-Id: Iead98670bb5f7627ae32f7ac41b4ebcee2726841 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3904427 Reviewed-by: Roman Lavrov <romanl@google.com> Reviewed-by: Cody Northrop <cnorthrop@google.com> Commit-Queue: Jamie Madill <jmadill@chromium.org>