ENH: Add `ensure_not_exists` to dask.utils.
ENH: Add `ensure_not_exists` to dask.utils.

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