add script to find docker tag from release version

ops/travis/helpers/find_staging_version.sh

@@ -0,0 +1,29 @@
+#!/bin/bash
+# Usage: find_staging_version.sh
+# returns the full image tag corresponding to the git tag name that shall be used
+
+# http://redsymbol.net/articles/unofficial-bash-strict-mode/
+set -euo pipefail
+IFS=$'\n\t'
+
+GIT_COMMIT_SHA=$(git show-ref -s ${TRAVIS_TAG})
+ORG=${DOCKER_REGISTRY}
+REPO="webserver"
+
+# get token
+echo "Retrieving token ..."
+TOKEN=$(curl -s -H "Content-Type: application/json" -X POST -d '{"username": "'${DOCKER_USERNAME}'", "password": "'${DOCKER_PASSWORD}'"}' https://hub.docker.com/v2/users/login/ | jq -r .token)
+
+# get list of repositories
+echo "Retrieving repository list ..."
+REPO_LIST=$(curl -s -H "Authorization: JWT ${TOKEN}" https://hub.docker.com/v2/repositories/${ORG}/?page_size=100 | jq -r '.results|.[]|.name')
+
+# output images & tags
+echo
+echo "Images and tags for organization: ${ORG}"
+echo
+IMAGE_TAGS=$(curl -s -H "Authorization: JWT ${TOKEN}" https://hub.docker.com/v2/repositories/${ORG}/${REPO}/tags/?page_size=100 | jq -r '.results|.[]|.name')
+for j in ${IMAGE_TAGS}
+do
+echo "  - ${j}"
+done