docker_api connection plugin (#40)

* Add basic docker_api connection test.

* Split AnsibleDockerClient into module-independent and module-specific part.

* Mention new connection plugin.

* Fix tests.

* Add first version of docker_api connection plugin.

* Linting.

* Fix references.

* Improve connection tests.

* Fix put_file for all Python versions.

* Fix fetch_file.

* Linting.

* Update plugins/connection/docker_api.py

Co-authored-by: Andrew Klychkov <aaklychkov@mail.ru>

* Move potential common code to module_utils / plugin_utils.

* Move socket_handler to plugin_utils.

* Fix typo.

Co-authored-by: Andrew Klychkov <aaklychkov@mail.ru>

plugins/plugin_utils/common.py

@@ -0,0 +1,33 @@
+# 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_collections.community.docker.plugins.module_utils.common import (
+    AnsibleDockerClientBase,
+    DOCKER_COMMON_ARGS,
+)
+
+
+class AnsibleDockerClient(AnsibleDockerClientBase):
+    def __init__(self, plugin, min_docker_version=None, min_docker_api_version=None):
+        self.plugin = plugin
+        super(AnsibleDockerClient, self).__init__(
+            min_docker_version=min_docker_version,
+            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 _get_params(self):
+        return dict([
+            (option, self.plugin.get_option(option))
+            for option in DOCKER_COMMON_ARGS
+        ])