gnu: openmpi: Update to 3.0.1.

* gnu/packages/mpi.scm (openmpi): Update to 3.0.1.
[arguments]: In 'remove-absolute' phase, adjust romio file name.
* gnu/packages/maths.scm (scalapack)[arguments]: Add
'set-test-environment' phase.
(slepc-openmpi)[arguments]: Likewise.
(mumps-openmpi)[arguments]: Likewise.
(superlu-dist)[arguments]: In 'check' phase, set
'OMPI_MCA_plm_rsh_agent'.
(scotch)[arguments]: In 'build-esmumps', likewise.
(p4est)[arguments]: Add 'set-test-environment' phase.
(hypre-openmpi)[arguments]: Likewise.