This includes two method for build rpm repo:
1. create the metadata in rootfs_rpm
2. standalone binary for building the metadata
Not both of them are needed, generally #2 fits more for the purpose,
but #1 may have its use on rootfs creation using zypper.
Both share some problems and are subjected for future improvement:
1. the createrepo now builds metadata for the whole directory,
if there are more than one arch, it builds for all, which means
rootfs_rpm may run longer if more builds have been run.
2. createrepo builds metadata for stale rpms
