Convert all HTML doc to RST

The motivation for this conversion is to have DevStack's docs be
generated using a more familair workflow for OpenStack projects, using
Sphinx.

Changing from raw HTML to RST will also make it easier to contribute
more documentation, as well as making edits less of a hassle.

The majority of the work was done by using Pandoc to convert from HTML
to RST, with minor edits to the output to remove errors in Sphinx.

Change-Id: I9636017965aeade37b950ddf5bdb0c22ab9004bd
Merge "Convert all HTML doc to RST"