asciidoc pulls in a lot of dependencies, most of those are not
needed as we just use it to convert txt to a man page. Adding
--no-install-recommended option to apt-get makes it skip those
additional dependencies. The only needed package is xmlto, so
let's add it explicitly.

This results is some 50 packages being skipped (mostly TeX/LaTeX and
some extra SGML tools), wow!
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>