FIX-#337: Fix MpiHosts parameter usage #767

Job	Run time
lint (black)	6s
lint (flake8)	6s
test-ubuntu (backend ray, python 3.8)	12m 24s
test-ubuntu (backend mpi, python 3.8)	15m 7s
test-ubuntu (backend dask, python 3.8)	17m 9s
test-ubuntu (backend pymp, python 3.8)	15m 54s
test-ubuntu (backend pyseq, python 3.8)	13m 43s
test-ubuntu (backend ray, python 3.9)	13m 12s
test-ubuntu (backend mpi, python 3.9)	14m 15s
test-ubuntu (backend dask, python 3.9)	13m 43s
test-ubuntu (backend pymp, python 3.9)	11m 18s
test-ubuntu (backend pyseq, python 3.9)	12m 6s
test-windows (backend ray, python 3.8)	10m 12s
test-windows (backend mpi, python 3.8)	13m 48s
test-windows (backend dask, python 3.8)	11m 28s
test-windows (backend pymp, python 3.8)	10m 28s
test-windows (backend pyseq, python 3.8)	14m 51s
test-windows (backend ray, python 3.9)	16m 48s
test-windows (backend mpi, python 3.9)	14m 16s
test-windows (backend dask, python 3.9)	16m 59s
test-windows (backend pymp, python 3.9)	12m 40s
test-windows (backend pyseq, python 3.9)	11m 33s
	4h 32m 6s

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