IoLoop: heartbeat should be sent when 50% of timeout elapsed
IoLoop: heartbeat should be sent when 50% of timeout elapsed

If heartbeat of 60 is configured, heartbeat should be sent every 30s
We shouldn't queue a heartbeat send, we should directly send it and wake the loop

Might fix #251

Signed-off-by: Marc-Antoine Perennou <07f76cf0511c79b361712839686f3cee8c75791c@Perennou.com>

Geal/lapin,sozu-proxy/lapin,Geal/lapin