docker_swarm_service_info: Read information about swarm services (#55008)

* Add docker_swarm_service_info module

* Remove unused import

* Limit to retrieving info about one service

* Add exists return value

* Add yaml 3-dash

Co-Authored-By: hannseman <hannes@5monkeys.se>

* Document return value as jinja `none´

Co-Authored-By: hannseman <hannes@5monkeys.se>

* Name is required

lib/ansible/modules/cloud/docker/docker_swarm_service_info.py

@@ -0,0 +1,104 @@
+#!/usr/bin/python
+#
+# (c) 2019 Hannes Ljungberg <hannes.ljungberg@gmail.com>
+# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
+
+from __future__ import absolute_import, division, print_function
+__metaclass__ = type
+
+
+ANSIBLE_METADATA = {
+    'metadata_version': '1.1',
+    'status': ['preview'],
+    'supported_by': 'community'
+}
+
+DOCUMENTATION = '''
+---
+module: docker_swarm_service_info
+
+short_description: Retrieves information about docker services from a Swarm Manager
+
+description:
+  - Retrieves information about a docker service.
+  - Essentially returns the output of C(docker service inspect <name>).
+  - Must be executed on a host running as Swarm Manager, otherwise the module will fail.
+
+version_added: "2.8"
+
+options:
+  name:
+    description:
+      - The name of the service to inspect.
+    type: str
+    required: yes
+extends_documentation_fragment:
+  - docker
+  - docker.docker_py_1_documentation
+
+author:
+  - Hannes Ljungberg (@hannseman)
+
+requirements:
+  - "L(Docker SDK for Python,https://docker-py.readthedocs.io/en/stable/) >= 2.0.0"
+  - "Docker API >= 1.24"
+'''
+
+EXAMPLES = '''
+- name: Get info from a service
+  docker_swarm_service_info:
+    name: myservice
+  register: result
+'''
+
+RETURN = '''
+exists:
+    description:
+      - Returns whether the service exists.
+    type: bool
+    returned: always
+    sample: true
+service:
+    description:
+      - A dictionary representing the current state of the service. Matches the C(docker service inspect) output.
+      - Will be C(none) if service does not exist.
+    returned: always
+    type: dict
+'''
+
+from ansible.module_utils.docker.swarm import AnsibleDockerSwarmClient
+
+
+def get_service_info(client):
+    service = client.module.params['name']
+    return client.get_service_inspect(
+        service_id=service,
+        skip_missing=True
+    )
+
+
+def main():
+    argument_spec = dict(
+        name=dict(type='str', required=True),
+    )
+
+    client = AnsibleDockerSwarmClient(
+        argument_spec=argument_spec,
+        supports_check_mode=True,
+        min_docker_version='2.0.0',
+        min_docker_api_version='1.24',
+    )
+
+    client.fail_task_if_not_swarm_manager()
+
+    service = get_service_info(client)
+
+    client.module.exit_json(
+        changed=False,
+        service=service,
+        exists=bool(service)
+    )
+
+
+if __name__ == '__main__':
+    main()