Provide openstack-dn2osdbk

This tool converts docutils native XML to docbook. The conversion is
done using XSLT, with some custom XML treatment.

The XSL source is a slightly modified version of Dn2dbk written by Éric
Bellot (http://ebellot.chez.com/dn2dbk/index.htm).

Modify doctest to check and build the HOT guide.

Implements: blueprint heat-templates

Change-Id: If866a5ffe19165c38981493684de550e0df0e36d
Merge "Provide openstack-dn2osdbk"