vmg: When using a power of two as process number, compute an own process distribution instead of relying on MPI_Dims_create (which produces non-standard conform results on Jugene).
git-svn-id: https://svn.version.fz-juelich.de/scafacos/trunk@1745 5161e1c8-67bf-11de-9fd5-51895aff932f