5c9a798324
After modernising docker configuration (I1215e04ec15b01c0b43bac8c0e81293f6724f278), we lost our registry-mirrors configuration in CI that lets us use a mirror of Dockerhub. This change uses the new docker_custom_config variable to configure the registry mirror. Change-Id: I1430413c12e9d0b59e4f216ff66372de0f3a4f21