Workaround Docker#42442 by using IPv4 SSH only

As described in moby/moby#42442,
docker daemon starts to expose a container port on different host ports
for IPv4 and IPv6 which breaks the ssh/safe-ssh/ansible backend
tests for some containers.
To prevent this behavior and flaky tests, only the first line from the
`docker port %s 22` command gets parsed to acquire the mapped SSH port.

Author: an-ky

test/conftest.py

@@ -113,7 +113,13 @@ def teardown():
         request.addfinalizer(teardown)
 
         port = check_output("docker port %s 22", docker_id)
-        port = int(port.rsplit(":", 1)[-1])
+        # IPv4 addresses seem to be reported consistently
+        # in the first line of the output.
+        # To workaround https://github.com/moby/moby/issues/42442
+        # use only the values of the first line of the command
+        # output
+        port = int(port.splitlines()[0].rsplit(":", 1)[-1])
+
         return docker_id, docker_host, port
 
     fname = "_docker_container_{}_{}".format(image, scope)