Avoid --user to support virtualenv

[jedbrown]

No description provided.

[baagaard-usgs]

This seems to only work for some installs.

We need a robust way to install to a specific directory that supports current Python module installation methods like Pip.

[jedbrown]

I think the centos-8 failure is a result of a pip that is older than 20.0.

Default to doing a user install (as if --user was passed) when the main site-packages directory is not writeable and user site-packages are enabled. -- https://pip.pypa.io/en/stable/news/#id303

Would you be willing to update pip in that container? Or activate a virtualenv in the default environment (which is what anyone setting up a non-containerized environment should want to do).

[baagaard-usgs]

Activating a virtualenv would lead to adding a virtualenv in the binary package too.

I can try a newer pip, but I think I tried 21.0 in a different situation and still had problems with things not ending up in the correct place.

[jedbrown]

You mean that the virtualenv would need to be activated to run pylith? That seems ... fine. It's a development environment.

[baagaard-usgs]

Addressed in PR #55