Some variables were not assigned values in the constructor.  This caused an "MPI_ERR_COMM: invalid communicator" error when using multiple gpus.

Merge branch 'developAnna' of https://git.rz.tu-bs.de/m.schoenherr/VirtualFluids_dev into developAnna

(cherry picked from commit d824fe1a)

automatically set para->useStreams to false for single gpu