If wcfs kills client that did not respond to pin notification in
pintimeout time, we need to wait strictly _more_ than that time to detect
whether client was killed or not. And in practice, due to noise in
operating system load and other factors, that waiting time should be
significantly greater to detect lack of expected event. However we were
waiting for exactly 1·pintimeout time and were claiming that there was
no pinkill event right after that.

-> Wait for 2·pintimeout instead of 1·pintimeout to make pinkill detection robust.

/reviewed-by @levin.zimmermann
/reviewed-on nexedi/wendelin.core!18