CI: run docker image as specified user
This is a feature request to be able to run a docker container in CI as a specified user (eg, to load up a specific user profile pre defined in the container).
This option would be similar to the docker-run --entrypoint option which is there already today.
Syntax:
```
image:
name: myimage:latest
entrypoint: [""]
user: user:group
```
From the docker-run manual:
```
-u, --user=""
Sets the username or UID used and optionally the groupname or GID for the specified command.
The followings examples are all valid:
--user [user | user:group | uid | uid:gid | user:gid | uid:group ]
Without this argument the command will be run as root in the container.
```
issue