REGTESTS: make use of HAPROXY_ARGS and pass -dM by default

Enabling memory poisonning is often pretty effective for detecting
uninitialized structure fields. Let's enable it by default and let
the user change the arguments at will (e.g. forcing some memory limits
or disabling a poller). This will work with the latest vtest version
to date (02a9bc1).
1 file changed