Merge branch 'jk/lsan-race-ignore-false-positive'

CI jobs that run threaded programs under LSan has been giving false
positives from time to time, which has been worked around.

This is an alternative to the jk/lsan-race-with-barrier topic with
much smaller change to the production code.

* jk/lsan-race-ignore-false-positive:
  test-lib: ignore leaks in the sanitizer's thread code
  test-lib: check leak logs for presence of DEDUP_TOKEN
  test-lib: simplify leak-log checking
  test-lib: rely on logs to detect leaks
  Revert barrier-based LSan threading race workaround