File _multibuild of Package petsc

<multibuild>
  <package>doc</package>
  <!-- <package>serial</package> -->
  <!-- <package>openmpi</package> -->
  <package>gnu-openmpi-hpc</package>
  <package>gnu-openmpi2-hpc</package>
  <package>gnu-openmpi3-hpc</package>
  <package>gnu-mvapich2-hpc</package>
  <package>gnu-mpich-hpc</package>
</multibuild>