- Correct names of built packages, the mpi flavors were lacking the
flavor specific name infix, i.e. all flavors were named identically.

- Add openmpi2 flavor
- BuildRequire netcdf-{mpi_flavor}-devel for MPI flavors
- Add Conflicts between flavors of python3 subpackage (all flavors
install into python_sitearch).

- Convert openmpi package to multibuild flavor
- Use correct mpi version - openmpi currently means openmpi, and not openmpi2/3
Otherwise, VTK depends on openmpi1 (HDF5, netcdf) and openmpi2/3 (direct)
- Remove several mpi BuildRequires in serial flavor

- Add python3-vtk to vtk-devel Requires, same as for vtk-java/tcl
- Remove empty testing subpackage
- Fix path to VTK_DATA_ROOT default directory

- Update to version 8.1.2
* Issue error if vtkAlgorithm::GetInputConnection called on wrong port
* Added explicit cast to pacify UBSan’s “implicit-integer-truncation”
* Make some orientation marker widget methods virtual
* vtkImageBlend bug fix for compound mode
* vtkFlyingEdges2D: Properly color multiple isocontour values
* Invoke DeletePointEvent before deleting vtkSeedWidget seed
* Fix compilation issue due to Python3.7 API change
* Fix bug where re-enabling seed widget wouldn't move existing seeds
- Fix python dependencies
- Test to make sure python package is importable
- Split out MPI version since the MPI version cannot be used
outside an MPI environment.