MINOR: haproxy: abort config parsing on fatal errors for post parsing hooks

MINOR: haproxy: abort config parsing on fatal errors for post parsing hooks

When pre-check and post-check postparsing hooks= are evaluated in
step_init_2() potential fatal errors are ignored during the iteration
and are only taken into account at the end of the loop. This is not ideal
because some errors (ie: memory errors) could cause multiple alert
messages in a row, which could make troubleshooting harder for the user.

Let's stop as soon as a fatal error is encountered for post parsing
hooks, as we use to do everywhere else.