quick hack demonstrating use of CmdCp easyblock to build VisIt

see subject
quite impressive, this one, since I've been told VisIt is half a nightmare to get it to build

this would need an easyblock to be done "properly" though, which resolves the `-j` issue

what's the `--vtk` about? we have support for building VTK stand-alone, is there a `--system-vtk` supported too?