Update alpine images to alpine 3.9
What does this MR do?
Updates our alpine-based Docker images to use Alpine 3.9 (released at 2019-01-29).
Why was this MR needed?
The new stable version is out. Let's be up-to-date then
Are there points in the code the reviewer needs to double check?
Does this MR meet the acceptance criteria?
- Documentation created/updated
- Added tests for this feature/bug
In case of conflicts with
master- branch was rebased