6484b9b026
rpm-distro element was trying to install bin programs into the image but it doesn't provide any. Move that logic into the yum element which provides the install-packages bin. Change-Id: Id5339fc7ffbef6327fe41f50a3e39ab30b6d0320
Provide yum specific image building glue.
RHEL/Fedora/CentOS and other yum based distributions need specific yum customizations.
Customizations include caching of downloaded yum packages outside of the build chroot so that they can be reused by subsequent image builds. The cache increases image building speed when building multiple images, especially on slow connections. This is more effective than using an HTTP proxy as a yum cache since the same rpm from different mirrors is often requested.