installation: untar libzmq in venv folder instead of /usr/local

[notapirate]

• on a linux-host docker build, the user can't write to /usr/local and installing pyzmq fails
• untar libzmq to venv instead
• normal installation also changed because it's sensible to have all pyzmq dependencies in the venv
• jukebox.Dockerfile: removing ZMQ_PREFIX=${PREFIX} since PREFIX variable doesn't exist in docker environment
• jukebox.Dockerfile: use ENV to set ZMQ_DRAFT_API

[AlvinSchiller]

Hi, thanks for your contribution.

My thoughts about this:

• To solve access rights in the docker build, the libzmq download and unpacking has to be done before the user is set.
• libzmq is not a python lib and so it does not belong in the venv, in my opinion. A venv is also designed to be reproducable by removing and reinstalling all python modules, which libzmq cant fullfill. The recommended installation for libzmq is via a package installer, but as we need to build it ourself, "/usr/local/" is the correct folder to place it.
  IF we would decide to not put it on system level, i would recommend to place it in a new folder in the project root, like .libs, but i am not aware of any problems with the current solution.
• Theres already a PR to address some problems with the docker setup (Fix Docker for pyzmq #2167), so i would suggest to bring this together (i think the problem with the access right is an important hint, which was missed there.

[notapirate]

* libzmq is not a python lib and so it does not belong in the venv, in my opinion. A venv is also designed to be reproducable by removing and reinstalling all python modules, which libzmq cant fullfill. The recommended installation for libzmq is via a package installer, but as we need to build it ourself, "/usr/local/" is the correct folder to place it.
  IF we would decide to not put it on system level, i would recommend to place it in a new folder in the project root, like `.libs`, but i am not aware of any problems with the current solution.

I'm not a python expert, so if you say that's something one doesn't do that's fine with me. My reasoning was that libzmq, though not a python package, is a python package dependency, but I haven't found a clear rule/suggestion on the web whether non-python dependencies should be put in the venv or not, so I'll just use your suggestion to untar as root to /usr/local in docker and leave the normal installation unchanged.

* Theres already a PR to address some problems with the docker setup ([Fix Docker for pyzmq #2167](https://github.com/MiczFlor/RPi-Jukebox-RFID/pull/2167)), so i would suggest to bring this together (i think the problem with the access right is an important hint, which was missed there.

OK so how does this work, I make the changes and create a merge request with MR #2167?

[AlvinSchiller]

OK so how does this work, I make the changes and create a merge request with MR #2167?

@pabera has created a new PR #2307, where all relevant changes from the different PRs will be gathered.
Feel free to test this change and give feedback :)

[notapirate]

PR #2307 works and fixes this issue, so I'm closing this PR, thanks @AlvinSchiller for your time to review this PR.