Not compatible with --user flag

[Ramblurr]

These docker images assume the builtin UID/GID for www-data. But this breaks in situations where the uid/gid needs to be controlled and passed in via --user (for example when mounting NFS volumes that require a certain uid).

This is relatively easy to fix.. here is an example PR from a similar PHP+agache/nginx-fpm https://github.com/nextcloud/docker/pull/1278/files

[asbiin]

Thank you @Ramblurr
Unfortunately, this solution is not working.
The user choosen with --user still need to have write access to /var/www/html/storage and /var/www/html/bootstrap/cache.

I've created a PR to test another solution, can you test it?