Add test cases to show bugs are fixed

* octahedron adds a fully trilinic test case
* dd121 adds a test case that will default to more
  ranks in a direction other than X (here, Y)

The reference data is generated with a "last known good" patch from
release-5-0 from before the fix for #1631 was introduced, not that it
really matters. The reference build is unaffected by any of the bugs,
because it runs single-core.

Refs #1631, #1656

Change-Id: I46c63a91aaae19a37bbe39e0c973cb9888019591