FIX-#337: Fix MpiHosts parameter usage #757

Job	Run time
lint (black)	6s
lint (flake8)	14s
test-ubuntu (backend ray, python 3.8)	17m 16s
test-ubuntu (backend mpi, python 3.8)	14m 52s
test-ubuntu (backend dask, python 3.8)	12m 14s
test-ubuntu (backend pymp, python 3.8)	9m 11s
test-ubuntu (backend pyseq, python 3.8)	13m 20s
test-ubuntu (backend ray, python 3.9)	10m 50s
test-ubuntu (backend mpi, python 3.9)	18m 18s
test-ubuntu (backend dask, python 3.9)	10m 41s
test-ubuntu (backend pymp, python 3.9)	10m 26s
test-ubuntu (backend pyseq, python 3.9)	10m 56s
test-windows (backend ray, python 3.8)	17m 9s
test-windows (backend mpi, python 3.8)	15m 20s
test-windows (backend dask, python 3.8)	8m 29s
test-windows (backend pymp, python 3.8)	18m 11s
test-windows (backend pyseq, python 3.8)	18m 9s
test-windows (backend ray, python 3.9)	16m 46s
test-windows (backend mpi, python 3.9)	11m 38s
test-windows (backend dask, python 3.9)	12m 17s
test-windows (backend pymp, python 3.9)	14m 3s
test-windows (backend pyseq, python 3.9)	14m 42s
	4h 35m 8s

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