Add a "readiness probe" to DIND in CI

.gitlab-ci/jobs/ci-cluster/.gitlab-ci.yml

@@ -27,6 +27,8 @@
     DOCKER_CERT_PATH: "$DOCKER_TLS_CERTDIR/client"
     DOCKER_DRIVER: overlay2
   before_script:
+    # Give docker-in-docker time to come alive
+    - i=0; while [ "$i" -lt 12 ]; do docker info &>/dev/null && break; sleep 5; i=$(( i + 1 )) ; done
     - docker network create ${CI_JOB_ID} --driver=bridge -o "com.docker.network.driver.mtu"="1450"
     - k3d cluster create ${CI_JOB_ID} --config tests/ci/k3d/config.yaml --network ${CI_JOB_ID}
     - until kubectl get deployment coredns -n kube-system -o go-template='{{.status.availableReplicas}}' | grep -v -e '<no value>'; do sleep 1s; done