File _multibuild of Package imb

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