vtk: add test and description
vtk: add test and description

This patch is inspired from #3517.
- It adds a description (slightly shorter to comply with the 80 chars limit of homebrew)
- It fixes some minor spacing problems detected by brew audit
- It adds a minimal test

Closes #3517

Closes #3617.

Signed-off-by: Dominique Orban <b6b12199b0ff1342bf41262c4fcd3a561907b571@gmail.com>

kozo2/homebrew-science,maplesond/homebrew-science,pditommaso/homebrew-science,dpo/homebrew-science,DabeDotCom/homebrew-science,heuermh/homebrew-science,andrewjpage/homebrew-science,philippbayer/homebrew-science,quantumsteve/homebrew-science,parcollet/homebrew-science