This was sometimes causing false positives, for example if site have
only one hit and this hit takes more than one second, apdex is 0% and
promise failed, it seems useful to at least have a way to disable.

We are discussed on !1716 (comment 225941)
an idea of introducing a "minimal number of hits" parameter to not
detect this false positive on sites that are not accessed enough to
calculate a meaningful apdex.