Code review comment for lp:~andreserl/maas/trunk-fpi

We have 2 completely separate components here:
 a.) maas
 b.) a fast path installer

There is a problem in that the fast path installer doesn't "live" anywhere. That will be addressed at a later date, and would then be addressed here by removal of any 'xinstall' reference in maas. We'll re-submit this branch with such a removal.

Maas will interface with this fast path installer via popen. Essentially running a command like:
  make-userdata-maas "--apt-proxy={{proxy}}" \
     "--dpkg-selections={{dpkg_set_selections_here}}" \
     "--finished-url={{node_disable_pxe_url}}" \
     "--finished-url-data={{node_disable_pxe_data}}" \
     "{{url_of_thing_to_install}}" "{{target_disk}}"

Having maas invoke that command itself, and making the output available in a preseed variable named 'xinstall_data' which is then rendered in a preseed wholly with '{{xinstall_data}}' is pointlessly complex and not modifiable by the end user.