Shrink and hard-code rlist for test with very small box

The size of the cutoff is not material for the functioning of this
test, but it was making twofold parallelism impossible in double
precision, and with GPUs, because the buffer is too large for
the box.

Change-Id: I564672f4b6709e1d2de0228d2c65fabebc569796
Merge release-4-6 into release-5-0

Conflicts (regenerated):
	complex/nbnxn_vsite/reference_d.edr
	complex/nbnxn_vsite/reference_d.log
	complex/nbnxn_vsite/reference_d.tpr
	complex/nbnxn_vsite/reference_d.trr
	complex/nbnxn_vsite/reference_s.edr
	complex/nbnxn_vsite/reference_s.log
	complex/nbnxn_vsite/reference_s.tpr
	complex/nbnxn_vsite/reference_s.trr

Change-Id: I27c83d06ddd9505cbab659401ff240de0a768a08
Fix setting (t)MPI ranks/processes

- Setting mpi_threads_ref caused errors because value is
  compared to numbers
- $mpi_processes_ref > $new_mpi_ranks caused tmpi threads to be
  set if now domain decomposition was found for <8

Change-Id: I350ae7f51c4cb34ea384471c4b07777fc9ff5533
Merge release-5-0 into master

Change-Id: I7377670885a9dcabecc13483ce65dfd65738bb8f