Revert "MPI cluster code"

This reverts commit 8d4ba1df99eb4f9b73b825a7667ce167d17fd98e, reversing
changes made to 42e5ab84854f41b4c9a68e64cdf682401cbd712f.
Revert "Commit from MPI cluster"

This reverts commit 42e5ab84854f41b4c9a68e64cdf682401cbd712f.
Revert 7314e84..57a21c4

This rolls back to commit 7314e841f28dd250d6c0a6826734e6ee31a6263a.