Upgrades to a newer docker version (18.03.1-ce) caused files created inside to be owned by root on alpine. It appears that the logic to set up the user in the container so that this doesn't happen was missing from alpine. While it's not clear why it worked before at all, the logic has been duplicated (tweaked for the alpine base image).
This change enables CLI build for Alpine 3.6 and also adds CI job for
it. It is mostly based on changes that were necessary to
enable building of rhel.6 CLI
