Avoid asserting that threading can not be in profile
Avoid asserting that threading can not be in profile

This fixes an intermittent failure in

    distributed/tests/test_worker.py::test_statistical_profiling_2

This is also occasionally possible if the thread is busy in concurrent.futures
code

dask/distributed,mrocklin/distributed,dask/distributed,dask/distributed,mrocklin/distributed,blaze/distributed,blaze/distributed,mrocklin/distributed,dask/distributed