Vendor API connection code from Docker SDK for Python (#398)

* Vendor parts of the Docker SDK for Python

This is a combination of the latest git version
(https://github.com/docker/docker-py/tree/a48a5a9647761406d66e8271f19fab7fa0c5f582)
and the version before Python 2.7 support was removed
(https://github.com/docker/docker-py/tree/650aad3a5fb84059b392ad450f760ed08143ae3f),
including some modifications to work with Ansible module_utils's
system (i.e. third-party imports are guarded, and errors are
reported during runtime through a new exception
MissingRequirementException).

* Create module_utils and plugin_utils for working with the vendored code.

The delete call cannot be called delete() since that method already exists from requests.

* Vendor more code from Docker SDK for Python.

* Adjust code from common module_utils.

* Add unit tests from Docker SDK for Python.

* Make test compile with Python 2.6, but skip them on Python 2.6.

* Skip test that requires a network server.

* Add changelog.

* Update changelogs/fragments/398-docker-api.yml

Co-authored-by: Brian Scholer <1260690+briantist@users.noreply.github.com>

* Minimum API version is 1.25.

Co-authored-by: Brian Scholer <1260690+briantist@users.noreply.github.com>

plugins/plugin_utils/common_api.py

@@ -0,0 +1,39 @@
+# Copyright (c) 2019-2020, Felix Fontein <felix@fontein.de>
+# 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
+
+
+from ansible.errors import AnsibleConnectionFailure
+from ansible.utils.display import Display
+
+from ansible_collections.community.docker.plugins.module_utils.common_api import (
+    AnsibleDockerClientBase,
+)
+
+from ansible_collections.community.docker.plugins.module_utils.util import (
+    DOCKER_COMMON_ARGS,
+)
+
+
+class AnsibleDockerClient(AnsibleDockerClientBase):
+    def __init__(self, plugin, min_docker_api_version=None):
+        self.plugin = plugin
+        self.display = Display()
+        super(AnsibleDockerClient, self).__init__(
+            min_docker_api_version=min_docker_api_version)
+
+    def fail(self, msg, **kwargs):
+        if kwargs:
+            msg += '\nContext:\n' + '\n'.join('  {0} = {1!r}'.format(k, v) for (k, v) in kwargs.items())
+        raise AnsibleConnectionFailure(msg)
+
+    def deprecate(self, msg, version=None, date=None, collection_name=None):
+        self.display.deprecated(msg, version=version, date=date, collection_name=collection_name)
+
+    def _get_params(self):
+        return dict([
+            (option, self.plugin.get_option(option))
+            for option in DOCKER_COMMON_ARGS
+        ])