[WIP] u3d/install: refactor towards supporting a U3D_INSTALL_PATH env variable

[lacostej]

Relates to #229

Lacks

• documentation
• unit tests
• cleanup WRT to change in variable
• decision WRT Mac target path support vs hardcoding '/'

[bdominguez]

@lacostej @niezbop How's this going? Now I pass the parameter "installation_path" that you have to indicate the path next to "Unity_VERSION".

I understand that this pull request improves this flow in terms of CI by only having to indicate the base path where all the directories of each version of the editor that would be built by u3d.

[niezbop]

@bdominguez I think that this PR is in quite a poor shape right now. As said in #382 , the Unity .pkg installer does not support paths but only volumes, which is the reason for FIXME: we don't support target_path anymore in this PR.

We would need to take decisions WRT Mac target path support vs hardcoding '/'. And the installer have had a few modifications since this PR was opened, so we may have to rebase it and work on it some more. There are already some conflicts in the file.

I don't have much time to work on this soon but I'll try to take a look at what's possible to do when I can.

[bdominguez]

Ok, thanks.