Execute basic integration tests against Certbot dockers during CI (#8396)

Fixes #8202

This PR adds an Azure Pipeline job to execute certbot plugins --prepare for each Docker image created during the CI on amd64.

* Prepare basic integration tests for certbot dockers

* Add a displayName for the integration tests task

.azure-pipelines/templates/jobs/packaging-jobs.yml

@@ -31,6 +31,25 @@ jobs:
           path: $(Build.ArtifactStagingDirectory)
           artifact: docker_$(DOCKER_ARCH)
         displayName: Store Docker artifact
+  - job: docker_run
+    dependsOn: docker_build
+    pool:
+      vmImage: ubuntu-18.04
+    steps:
+      - task: DownloadPipelineArtifact@2
+        inputs:
+          artifact: docker_amd64
+          path: $(Build.SourcesDirectory)
+        displayName: Retrieve Docker images
+      - bash: set -e && docker load --input $(Build.SourcesDirectory)/images.tar
+        displayName: Load Docker images
+      - bash: |
+          set -ex
+          DOCKER_IMAGES=$(docker images --filter reference='*/certbot' --filter reference='*/dns-*' --format '{{.Repository}}:{{.Tag}}')
+          for DOCKER_IMAGE in ${DOCKER_IMAGES}
+            do docker run --rm "${DOCKER_IMAGE}" plugins --prepare
+          done
+        displayName: Run integration tests for Docker images
   - job: installer_build
     pool:
       vmImage: vs2017-win2016