Expand environment variables in file pointed at by LMOD_MODULEPATH_INIT

[runiq]

We currently have most of our Lmod config on a shared filesystem /shared/etc/lmod, so we can change the config without having to rebuild our node images. This also works with the initial modulepath, because we have $LMOD_MODULEPATH_INIT point at /shared/etc/lmod/modulepath.

Unfortunately, the file pointed at by $LMOD_MODULEPATH_INIT doesn't allow expansion of environment variables, which would be valuable for adding module hierarchies in users' home directories.

Would you consider adding environment variable support for the $LMOD_MODULEPATH_INIT file, for example by using envsubst (from the gettext software)?

[rtmclay]

I will consider it but I'd like you to create a PR to show what you want. Make sure that it works when envsubst is not in $PATH.