The byjg/easy-haproxy image polls Docker for label changes every 10
seconds by default, which races with the haproxy bats suite and
intermittently produces curl exit 7. Expose `refresh-conf` as a
global-only haproxy property that maps to `EASYHAPROXY_REFRESH_CONF`,
lower it to 2 seconds in the bats setup, and wrap the localhost HTTP
assertions in a retry loop so checks wait for haproxy to converge
rather than failing on the first attempt.
