web: properly handle acme.sh return codes

It exits with 2 in case a renew is not necessary.

web/rootfs/etc/cont-init.d/10-config

@@ -23,13 +23,15 @@ if [[ $DISABLE_HTTPS -ne 1 ]]; then
             fi
             export LE_WORKING_DIR="/config/acme.sh"
             # TODO: move away from standalone mode to webroot mode.
-            if ! /config/acme.sh/acme.sh \
+            /config/acme.sh/acme.sh \
                 $STAGING \
                 --issue \
                 --standalone \
                 --pre-hook "if [[ -f /var/run/s6/services/nginx ]]; then s6-svc -d /var/run/s6/services/nginx; fi" \
                 --post-hook "if [[ -f /var/run/s6/services/nginx ]]; then s6-svc -u /var/run/s6/services/nginx; fi" \
-                    -d $LETSENCRYPT_DOMAIN ; then
+                -d $LETSENCRYPT_DOMAIN
+            rc=$?
+            if [[ $rc -eq 1 ]]; then
                 echo "Failed to obtain a certificate from the Let's Encrypt CA."
                 # this tries to get the user's attention and to spare the
                 # authority's rate limit: