Re implement the rootfs generation using rpm5.  This also gets rid of the
need for yum, and handles all dep resolving internal to the script itself.

The new file scripts/rootfs_rpm-extract-postinst.awk comes from the original
yum integration work.  It has been unchanged, but since yum is no longer used
we needed to move the script somewhere else.

Signed-off-by: Mark Hatle <mhatle@windriver.com>