Update the upgrade design document according to the outcome
of the design discussion at GanetiCon 2013. There are two
changes in the design.

* As revision upgrades are binary compatible at all levels,
  one can accept a rough upgrade, just replacing the binaries.
  Therefore, it will become a configure option whether version
  includes revision and suffix, or not.

* The install/uninstall scripts are replaced in favor of another
  level of indirection. In this way, at run time, only two symlinks
  in ${sysconfdir}/ganeti, will be changed, whereas links under
  ${PREFIX}/bin, ${PREFIX}/sbin, and similar, are not touched by
  ganeti itself.

* The layout for the ganeti python libraries, which do not provide
  stable interface, are changed to be used as private modules.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Apollon Oikonomopoulos <apoikos@gmail.com>
Reviewed-by: Michele Tartara <mtartara@google.com>