Switch es hadoop docs to direct_html

[nik9000]

direct_html is faster and more customizable. It is the future!

[nik9000]

This PR will make a diff and I'll check the diff. If it looks good then I'll merge this. If it doesn't I'll iterate on --direct_html until it does.

[nik9000]

That particular failure is one that I've been trying to fix in the source repos. I'll open a PR.

[nik9000]

elastic/elasticsearch-hadoop#1408 will fix the error!

[nik9000]

@elasticmachine, run elasticsearch-ci/docs

[nik9000]

This needs:

• Support for "center" and "middle" on images. (see 2.2/ey-usage.html) (Ignore some defaults in direct_html comparison #1586)
• Strip html from the summary of tables (Clean html from the table summary in direct_html #1583)
• Fix rendering of duplicate callouts (Improve rendering of callout lists in direct_html #1582)
• Figure out what is up with stuff like <a class="indexterm" id="id-1.13.7.25.1"></a>. We almost certainly don't need it. If so, ignore it in the diff. (Ignore unneeded tags in diffs for direct_html #1585)

[nik9000]

Diff looks good!

@jbaiera, please add --direct_html the next time you build the docs.

[nik9000]

And pull the docs repo!