Clean up performance report test (#3655)
Clean up performance report test (#3655)

Previously all of the text in the assertions was being included in the
performance report itself (ever since we started including the
surrounding frame).  This made these tests pass trivially.

Now we wrap the performance report in a function of its own.
dask/distributed,blaze/distributed,dask/distributed,dask/distributed,blaze/distributed,dask/distributed