use curl to test availability of ACME server, which tries all resolved IPs

[merlinran]

Fixes #3639

Tested in my gateway container.

docker compose exec -ti gateway /bin/sh
...
/app # nc -z localhost 80; echo $?
1
/app # nc -z 127.0.0.1 80; echo $?
0
/app # nc -z ::1 80; echo $?
1
/app # curl -sSf http://localhost > /dev/null; echo $?
0

Even with this fix, it may still fail to get the certificate, if the host has only IPv6 address, because this line listens only on IPv4 somehow.

shellhub/gateway/entrypoint.sh

Line 71 in 12e5116

ACME_WEBSERVER_PID=$(cd $ACME_WEBSERVER_ROOT; python -m http.server 80 > /dev/null 2>&1 & echo $!)

Even though the Python3 doc says

By default, the server binds itself to all interfaces. The option -b/--bind specifies a specific address to which it should bind. Both IPv4 and IPv6 addresses are supported.

[gustavosbarreto]

Merged! Thanks @merlinran