Docker: Allow to configure shared memory size

Merged username-removed-259801 requested to merge doits/gitlab-ci-multi-runner:shm_size into master

What does this MR do?

Allow to set shared memory size for docker images.

Why was this MR needed?

Docker by default uses a shared memory size of 64m. Some images benefit from a bigger shared memory size, though. For example the docker selenium images recommend to mount shared memory space to fix crashes due to too low shared memory size. With this MR, the shared memory size can be increased with a config option.

Are there points in the code the reviewer needs to double check?

This is based on top of !301 (merged) because the current used (outdated) dockerclient does not support the ShmSize, so !301 (merged) has to be merged in first. Changes on top of that are really small - just passing through the new config option.

Does this MR meet the acceptance criteria?

  • Documentation created/updated
  • Tests
    • Added for this feature/bug
    • All builds are passing
  • Branch has no merge conflicts with master (if you do - rebase it please)

What are the relevant issue numbers?

Fixes #1913 (closed)