So far, the Tobiko docs were duplicated in some places, different
(although duplicated), and some fragments were not relevant (or
outdated).
This patch refactors the Tobiko test cases run guide by modularizing
the fragments ("spilling" fragments instead of coping them),
correcting typos, and deleting/updating irrelevant information.
Note: in order to see how the change will appear, download it with
`git review -d <change_url>`, run the `tox -e docs` command, and then
double click
(with the file explorer) tobiko/doc/build/html/<file-you-want>.
Change-Id: I4c8ba2cb89075ef25afd77fedeaed8a896df74e7
87999de932