remove racy test assertions

Do not assert before the loop waiting for the thread to complete the
expected side effect. The whole point of the loop is to make sure
there is no window of opportunity for a race condition and asserting
before it means taking a useless risk. If run enough times, it will
happen.

Signed-off-by: Loic Dachary <loic@dachary.org>
Merge pull request #499 from dachary/wip-test_osd_types

remove racy test assertions