Install script does not install modules

The duneci-install-module has an unfortunate name. It suggests that it installs the module while it actually builds it.

• Yes, I know that this is the traditional procedure on dune modules.
• Yes, I know that most people do not care about installing dune but building it.

Still, would be good to have a script that actually checks that the installation procedure actually works. If you ask me, I would even be bold to say that the script should install new modules based on the installed ones (i.e. without the build). As a matter of fact, the installation process is currently working because is something required to provide spack packaging.

The solution to the script looks pretty easy. Let me know if you are interseted I make a MR.