Tests: Wait for the minio-server to initialize before using it

This should help fix flakiness we're seeing with webresources where
tests fail because we try to create the bucket before the minio server
has initialized and therefore it causes test failures. This also adds
a `set -e` so that if the command does still fail it should fail fast
rather than after trying to run all the tests, and make it clearer
where the error actually originates from

Change-type: patch

docker-compose.test-custom.yml

@@ -38,6 +38,11 @@ services:
     entrypoint: >
       /bin/sh -c "
       set -e;
+
+      while ! curl -I minio-server:9000/minio/health/live; do
+          sleep 1;
+      done
+
       /usr/bin/mc config host add minio-server http://minio-server:9000 USERNAME PASSWORD;
       /usr/bin/mc mb --ignore-existing minio-server/balena-pine-web-resources;
       sleep infinity;