Run docker-s3fs-client as non root user

[donovat]

I agree with another user, thank you for providing (and maintaing!) this docker image.
I am currently testing using the image on an Red Hat OpenShift cluster. This is to by pass the requirement to have the s3fs code installed directly on the cluster.
One of the main security objectives is to run the containers with the OpenShift Cluster as a non root user. I understand that it can be set if required, although a lot of admin staff do get upset. Thus trying to run with either a random or per-defined UID/GID.
Normally with storage you can get a way with just using a GID of '0'.
However, in this case a lot of the commands in the docker-entrypoint.sh require root permission to execute.

Any Chance we could get extra flags or recommendations on how to run the image as a non root user.
ps. You can test by adding a USER setting at the end of the current docker file.