DOC: Be more explicit about configurable check ok/error/timeout status

DOC: Be more explicit about configurable check ok/error/timeout status

It is possible to configure the check status on success, on error and on
timeout, for http-check and tcp-check expect rules. But the documentation relies
on internal names. These names are reported on the stats and are describe in the
management guide. But it is probably a good idea to be more explicit too in the
doc describing these options.