Cloned from launchpad blueprint https://blueprints.launchpad.net/tripleo/+spec/tripleo-diskimage-builder-parallel-builds. Description: Background: Currently if you run parallel builds for diskimage-builder on a system the builds fail, because the diskimage-builder uses the common “~/.cache/image-create” directory to cache OS image files, git repositories, Python or Ruby packages etc. to create the images. Proposal: If we want to enable parallel builds, then we need to identify and tie the builds to the correct “~/.cache/image-create” folder. To do this we can use mktemp and let diskimage-builder use this directory as the cache directory instead of “DIB_IMAGE_CACHE” (~/.cache/image-create). export CACHE_DIR=$(mktemp -d ~/.cache/image-create.XXXXXXXX) This will create the "~/.cache/image-create.XXXXXXXX" directory and let the diskimage-builder use it for its respective builds. Also, to enable diskimage-builder to build with the correct "~/.cache/image-create.XXXXXXXX" directory for “--offline” mode; the script should force the user to specify the respective “image-create.XXXXXXXX” folder to refer to for the build. Specification URL (additional information): None