small steps to make CreatePartitionTopology deterministic
The master branch contains a bunch of modifications that makes partitioning deterministic, provided that we don't create the partition topology.
This branch contains additional changes that aim at making CreatePartitionTopology deterministic, but it is clearly incorrect (test e.g. "gmsh tutorial/t5.geo -saveall -part 2")
So it's not ready for merging, but let's keep it here for future reference.