head-node: Build {petsc,slepc}-openmpi.

* head-node.scm (cuirass-specs): In ‘guix’ spec, add “petsc-openmpi” and
“slepc-openmpi”.

head-node.scm

@@ -221,6 +221,7 @@ export CUIRASS_LOGGING_LEVEL=${CUIRASS_LOGGING_LEVEL:-debug}\n"
                        (build '(packages "gcc-toolchain" "openmpi" "mpich"
                                          "hwloc" "intel-mpi-benchmarks"
                                          "petsc" "slepc"
+                                         "petsc-openmpi" "slepc-openmpi"
                                          "python-scipy" "scotch" "pt-scotch"
                                          "metis" "mumps" "mumps-metis"
                                          "mumps-metis-openmpi" "mumps-openmpi"