snappyHexMesh consistent parallel v.s. serial refinement

Functionality to add/problem to solve

When running snappyHexMesh in parallel it might not give the exact same result as running non-parallel

Proposal

Run serial and parallel side-by-side. Make sure refinement is exactly the same.

E.g. Tutorial mesh/snappyHexMesh/gap_detection and have random decomposition.

See also https://exchange.openfoam.com/node/1691.

What does success look like, and how can we measure that?

Better parallel consistent behaviour. There might still be areas which are not exactly the same just due to e.g. the truncation errors in calculating the face- and cell-centres (different point ordering or orientation of face on processor patch, different ordering of faces in cell)