MAJOR: check: find out which port to use for health check at run time

HAProxy used to deduce port used for health checks when parsing configuration
at startup time.
Because of this way of working, it makes it complicated to change the port at
run time.

The current patch changes this behavior and makes HAProxy to choose the
port used for health checking when preparing the check task itself.

A new type of error is introduced and reported when no port can be found.

There won't be any impact on performance, since the process to find out the
port value is made of a few 'if' statements.

This patch also introduces a new check state CHK_ST_PORT_MISS: this flag is
used to report an error in the case when HAProxy needs to establish a TCP
connection to a server, to perform a health check but no TCP ports can be
found for it.

And last, it also introduces a new stream termination condition:
SF_ERR_CHK_PORT. Purpose of this flag is to report an error in the event when
HAProxy has to run a health check but no port can be found to perform it.
5 files changed