Adding MPI_LINK_FLAGS to sandbox-test when applicable
Adding MPI_LINK_FLAGS to sandbox-test when applicable

justusc/Elemental,birm/Elemental,birm/Elemental,justusc/Elemental,justusc/Elemental,justusc/Elemental,mcopik/Elemental,mcopik/Elemental,birm/Elemental,mcopik/Elemental,mcopik/Elemental,justusc/Elemental,mcopik/Elemental,birm/Elemental,birm/Elemental,birm/Elemental,justusc/Elemental,mcopik/Elemental