tweak the wait script.

docker/README.md

@@ -0,0 +1 @@
+`rootfs`  is only used by Dockerfile and Dockerfile.collector

rootfs/etc/services.d/collector-once/run

@@ -7,8 +7,7 @@ s6-svwait -u /var/run/s6/services/scrutiny
 s6-svc -O /var/run/s6/services/collector-once
 
 # wait until scrutiny is "Ready"
-while [[ "$(curl -s -o /dev/null -w ''%{http_code}'' http://localhost:8080/api/health)" != "200" ]]; do sleep 5; done
-
+until $(curl --output /dev/null --silent --head --fail http://localhost:8080/api/health); do echo "not ready" && sleep 5; done
 
 echo "starting scrutiny collector"
 /scrutiny/bin/scrutiny-collector-metrics run