Use minio to store ccache objects

The gitlab-runner code is notoriously bad at storing large amounts of cache objects since it tries to compress all of them and uses zip. The ccache objects are already compressed and zip is inefficient.

Instead, store cache in minio by making an uncompressed tarball directly to stdout. Restore the cache by downloading the tarball and extracting on the fly.

Also, use the ramdisk that is included with our build containers in /opt/ramdisk for extra performance.