BUG/MEDIUM: checks: make sure the warmup task takes the server lock

The server warmup task is used when a server uses the "slowstart"
parameter. This task affects the server's weight and maxconn, and may
dequeue pending connections from the queue. This must be done under
the server's lock, which was not the case.

This must be backported to 1.9 and 1.8.
1 file changed