Add reverse member to start.test_start JSON, which is 1 in --reverse mode.

This lets us tell easily from the JSON output whether a test was run in
--reverse mode or not.  Resolves #167 (one comment made in that issue
anyway).

(cherry picked from commit ef3eae69bff269767287a9bc9e7c98c2460ae382)
Signed-off-by: Bruce A. Mah <bmah@es.net>