Make test to verify that download of gcr image works

[Glenn-Terjesen]

Make test to verify that download of gcr image works in the Dockerfile during the build step

[Glenn-Terjesen]

todo: Need to build a dockerfile that download a gcr authenticated image in the FROM line

[xamebax]

This was exported to JIRA and will be followed-up there: https://entur.atlassian.net/browse/CLOUD-4177