Use the zipper implementation when traversing a test suite
Use the zipper implementation when traversing a test suite

The run' function is now tail recursive, and will be easier to convert
to use continuation passing.

Signed-off-by: John Else <37b74501daa612e48fea94f9846ed4ddeb6a8f07@citrix.com>

johnelse/ocaml-webtest,johnelse/ocaml-webtest,johnelse/ocaml-webtest