tests/qapi/doc-good.json: Prepare for qapi-doc Sphinx extension

doc-good.json tests doc comment parser corner cases.  We're about to
largely replace it by a Sphinx extension, which will have different
corner cases.  Tweak the test so it passes both with the old parser
and the Sphinx extension, by making it match the more restrictive
rST syntax:

 * in a single list the bullet types must all match
 * lists must have leading and following blank lines
 * the rules on when and where indentation matters differ
 * the '|' example syntax is going to go away entirely, so stop
   testing it

This will avoid the tests spuriously breaking when we tighten up the
parser code in the following commits.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20200925162316.21205-4-peter.maydell@linaro.org>
Signed-off-by: Markus Armbruster <armbru@redhat.com>