Policies for initrd.img and install.img image generation.

lorax takes a different approach than the previous buildinstall set of scripts
for generating the boot and install images and tree data files.  First, the
main ideas:

    * Configuration files control the list of packages to make images with.

    * Rather than explicitly listing the files to keep in the images (i.e.,
      we used to have KEEPFILE variables in upd-instroot), we now take what
      the packages lay down and do a minimal tree scrubbing (remove docs,
      for example).  This is customizable through configuration files
      because we will always have exceptions.  But the policy in lorax is
      opposite of the buildinstall policy:  take everything that RPMS lay
      down, remove what we don't want--rather than removing everything
      that is not explicitly listed in KEEPFILE variables.

    * The main root tree generated from the package set is broken in to
      /usr for the install.img and everything else for the initrd.img.
      This is configurable through configuration files since we will
      always have exceptions.

    * Static data such as files we need to place in /etc in the images or
      other control files are stored in /usr/share/lorax and copied in to
      the image staging tree.

The approach of taking what the packages give us is a decision to make
maintenance of the image building tools easier.  Whatever the packages lay
down should be sufficient for the installation images and we shouldn't
have to have our own list of files to keep and library gathering routines.
Let the packaging tools figure that out.

The whole tool is written in Python with a driver program ("lorax"), but the
actual logic for the program is in the pylorax module.  The idea behind this
is that tools such as pungi can potentially import pylorax directly and not
have to run the command line tool to do image generation work.  That is,
pungi can use lorax programatically.

This tool is still in the early stages of development (Sep 2008) and patches
and comments are welcome.