* Clean up unnecessary vertical quotes at the left side
caused by extra spaces at the beginning of lines.
* Do not use backquotes in the title lines
(ref/run_tests.rst, ref/horizon.rst)
When backquotes are used in the first-level title,
it will be included in the navigation at the top-right corner
https://docs.openstack.org/developer/horizon/contributor/ref/index.html
* Remove duplicated contents:: directive in ref/run_tests.sh.
openstackdocstheme generates the toc by default, so having contents::
directive leads to duplicated toc in a page.
Change-Id: Icc641927ad7cd7a8d79632c64a3ce212f0dc0b64
