Fix implicit string concatenation in Popen args (#514)
Fix implicit string concatenation in Popen args (#514)

Also removed the `--scheduler` argument which caused problems for some users
amosonn/distributed,blaze/distributed,dask/distributed,mrocklin/distributed,amosonn/distributed,dask/distributed,amosonn/distributed,blaze/distributed,broxtronix/distributed,broxtronix/distributed,dask/distributed,mrocklin/distributed,broxtronix/distributed,dask/distributed,mrocklin/distributed