Add docker_context_info module (#1039)

* Vendor parts of the Docker SDK for Python

This is a combination of the latest git version
(https://github.com/docker/docker-py/tree/db7f8b8bb67e485a7192846906f600a52e0aa623)
with some fixes to make it compatible with Python 2.7
and adjusting some imports.

* Polishing.

* Fix bug that prevents contexts to be found when no Docker config file is present.

Ref: https://github.com/docker/docker-py/issues/3190

* Linting.

* Fix typos.

* Adjust more to behavior of Docker CLI.

* Add first iteration of docker_context_info module.

* Improvements.

* Add basic CI.

* Add caveat on contexts[].config result.

plugins/module_utils/_api/utils/utils.py

@@ -303,12 +303,7 @@ def parse_host(addr, is_win32=False, tls=False):
     if proto in ('tcp', 'ssh'):
         port = parsed_url.port or 0
         if port <= 0:
-            if proto != 'ssh':
-                raise errors.DockerException(
-                    'Invalid bind address format: port is required:'
-                    ' {0}'.format(addr)
-                )
-            port = 22
+            port = 22 if proto == 'ssh' else (2375 if tls else 2376)
             netloc = '{0}:{1}'.format(parsed_url.netloc, port)
 
         if not parsed_url.hostname: