fix test_scheduler to work w heartbeat registration
fix test_scheduler to work w heartbeat registration

jakirkham/dask,ssanderson/dask,mrocklin/dask,ContinuumIO/dask,chrisbarber/dask,jayhetee/dask,clarkfitzg/dask,wiso/dask,cowlicks/dask,pombredanne/dask,simudream/dask,mraspaud/dask,blaze/dask,PhE/dask,gameduell/dask,jakirkham/dask,dask/dask,cpcloud/dask,mraspaud/dask,jcrist/dask,jayhetee/dask,jcrist/dask,ssanderson/dask,vikhyat/dask,wiso/dask,clarkfitzg/dask,vikhyat/dask,simudream/dask,mikegraham/dask,blaze/dask,pombredanne/dask,dask/dask,mrocklin/dask,PhE/dask,ContinuumIO/dask