Rewrite Elasticsearch AsciiDoc chapter

Reorganized and expanded to cover the new
index.search.interface=... configuration approach to ES alongside the
old legacy ES configuration settings
Tweak AsciiDoc admonition block styles
Tweak ES INDEX_DIRECTORY handling, config tests

ES now just checks whether the config has an explicit value for
INDEX_DIRECTORY instead of checking whether any of the path.data,
path.work, and path.logs settings are present.

Adding some new test cases to exercise Elasticsearch data/work/logs
directory configuration behavior described in the docs.