Fix the empty user name when run in Docker

[Zarquan]

When we run the container in Docker we need to supply a uid so that files created inside the container don't end up being owned by root outside the container.

docker run \
    --user 1000 \
    ....

This means the shell inside the container is run with uid 1000, but there is no matching entry in the user or group database, so the shell prints a warning about the group and sets the user name to I have no name!.

groups: cannot find name for group ID 1000
I have no name!

There is nothing wrong with running a process using a uid and gid with no description, they are just numbers, but it would be good to avoid the warning and set the user name to something sensible.