(cherry picked from commit 553641f)

Default user and group id is now 977 as 999 was taken.
!!**This may cause permissions issues in existing installations**. These issues can be fixed by either:
- mounting the volume with another container as a root user and changing ownership of `/app/data` (including their contents) to 977:977
- `chmod -R 977:977 /var/lib/docker/volumes/${VOLUME_NAME_OR_HASH}` of the volume from the host's volume directory.
- `chmod -R  777 /app/data` (don't do this)

Dockerfile and entrypoint.sh was changed to run NO application code as a privileged user. When the container is running there is no code executed in a privileged context, as anything requiring privileges is run during build time.

Proposed Solution to dzikoysk#2288