For http-check send rules, it is now possible to use a log-format string to set
the request's body. the keyword "body-lf" should be used instead of "body". If the
string eval fails, no body is added.
For http-check send rules, it is now possible to use a log-format string to set
the request URI. the keyword "uri-lf" should be used instead of "uri". If the
string eval fails, we fall back on the default uri "/".