* Run node 10 with '--experimental_worker' flags
* Use dedicated function to retrieve node/npm program version
The goal of this commit is to ensure that any linux based node 10 deployments run with the experimental_worker flag. This flag is required for workers to "work" in node 10. This will not affect other versions of node. This resolves#4335 where Docker would fail due to being based on node 10.
Before this change, the docker user had home in a directory it had no
permissions on. The inability of creating a cache directory in `$HOME`
prevented npm to work properly.
Additionally, the `node_modules` in the base working directory had its
owner set to root, preventing further changes.
With this change, the `etherpad` user has a home directory.
Additionally, `npm i` is now run by `etherpad` rather than the root
user; this way, it is possible to dynamically change the `node_modules`
content in day 2 operations.
Note that while switching to the `useradd` builtin, a conflict was
discovered with the GID 65534 that was previously used. This change is
changing the `etherpad` user's UID to 5001 to avoid said conflict. As a
consequence, a `chmod -R 5001:5001` must be run prior to attaching
volumes created from previous Etherpad versions.
With this change, the Dockerfile builds the Docker image from the code
checked out in the local filesystem, instead of downloading a revision
from git.
Implements #3657
Richard Hansen