Utkarsh Ayachit authored Feb 27, 2019 and Ben Boeckel committed Mar 15, 2019

1. visit_gmv, visit_cgns reader seem to no exist anymore, hence removing
   options for them.
2. mpi4py module is enabled automatically by VTK/ParView hence no need
   to explicitly request it.
3. update various cmake variable names that have changed or removed.