BUG/MINOR: peers: Possible unexpected peer seesion reset after collisions.

BUG/MINOR: peers: Possible unexpected peer seesion reset after collisions.

During a peers session collision (two peer sessions opened on both side) we must
mark the peer the session of which will be shutdown as alive, if not ->reconnect
timer will be set with a wrong value if the synchro task expires after the peer
has been reconnected. This possibly leads to unexpected deconnections during handshakes.
Furthermore, this patch cancels any heartbeat tranmimission when a reconnection
is prepared.

(cherry picked from commit 6e1a9c57c938360e95f445e800f0d22782bb6c22)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>