Update openstack-doc-tools for translation of api-site

Version 0.13 of openstack-doc-tools is needed for building localized
books in the repo api-site, update the required version.

Significant changes between 0.11 and 0.13 are:
* ``openstack-generate-docbook`` handles now the api-site project.
* ``openstack-doc-test``: Handle changes in api-site project, new
  option --print-unused-files.
* ``openstack-autohelp``: Handle keystone_authtoken options.

Change-Id: I08677bbb08097f3b023515e9031f28a8da94ba67
Merge "Update openstack-doc-tools for translation of api-site"