Rework the create script

Rework the create script

This patch changes much of the internals of the create script:
  - we no longer harcode the variables suite, extrapkgs, mirror, etc.
    but instead read them from a config file
  - since we can install multiple suited, the cache filename is
    arch and suite dependant
  - ship a defaults file (but do not install it, that is easier done in
    the packaging)

The defaults file does not have any extra settings activated, so the
default values from the create script will be used. The patch also
changes the script to install in this default mode debian lenny and not
etch.

Reviewed-by: imsnah