Prepare docker tests for AZP. (#1482)

Backport of important parts of https://github.com/ansible-collections/community.docker/pull/48 to stable-1.

tests/integration/targets/setup_docker_registry/tasks/setup-frontend.yml

@@ -11,10 +11,18 @@
     name: '{{ docker_registry_container_name_frontend }}'
     image: "{{ docker_test_image_registry_nginx }}"
     ports: 5000
+    # `links` does not work when using a network. That's why the docker_container task
+    # in setup.yml specifies `aliases` so we get the same effect.
     links:
     - '{{ docker_registry_container_name_registry }}:real-registry'
     volumes:
     - '{{ docker_registry_container_name_frontend }}:/etc/nginx/'
+    network_mode: '{{ current_container_network_ip | default(omit, true) }}'
+    networks: >-
+      {{
+        [dict([['name', current_container_network_ip]])]
+        if current_container_network_ip not in ['', 'bridge'] else omit
+      }}
   register: nginx_container
 
 - name: Copy static files into volume
@@ -65,9 +73,17 @@
     debug:
       var: nginx_container.container.NetworkSettings
 
+  - name: Get registry URL
+    set_fact:
+      # Note that this host/port combination is used by the Docker daemon, that's why `localhost` is appropriate!
+      # This host/port combination cannot be used if the tests are running inside a docker container.
+      docker_registry_frontend_address: localhost:{{ nginx_container.container.NetworkSettings.Ports['5000/tcp'].0.HostPort }}
+      # The following host/port combination can be used from inside the docker container.
+      docker_registry_frontend_address_internal: "{{ nginx_container.container.NetworkSettings.Networks[current_container_network_ip].IPAddress if current_container_network_ip else nginx_container.container.NetworkSettings.IPAddress }}:5000"
+
   - name: Wait for registry frontend
     uri:
-      url: https://{{ nginx_container.container.NetworkSettings.IPAddress }}:5000/v2/
+      url: https://{{ docker_registry_frontend_address_internal }}/v2/
       url_username: testuser
       url_password: hunter2
       validate_certs: false
@@ -76,10 +92,6 @@
     retries: 5
     delay: 1
 
-  - name: Get registry URL
-    set_fact:
-      docker_registry_frontend_address: localhost:{{ nginx_container.container.NetworkSettings.Ports['5000/tcp'].0.HostPort }}
-
 - set_fact:
     docker_registry_frontend_address: 'n/a'
   when: can_copy_files is failed

tests/integration/targets/setup_docker_registry/tasks/setup.yml

@@ -44,6 +44,15 @@
       name: '{{ docker_registry_container_name_registry }}'
       image: "{{ docker_test_image_registry }}"
       ports: 5000
+      network_mode: '{{ current_container_network_ip | default(omit, true) }}'
+      # We need to define the alias `real-registry` here because the global `links`
+      # option for the NGINX containers (see setup-frontend.yml) does not work when
+      # using networks.
+      networks: >-
+        {{
+          [dict([['name', current_container_network_ip], ['aliases', ['real-registry']]])]
+          if current_container_network_ip not in ['', 'bridge'] else omit
+        }}
     register: registry_container
 
   - name: Get registry URL