Modify expand_registry_url to support v2 private registries.

docker/auth/auth.py

@@ -29,7 +29,7 @@ DOCKER_CONFIG_FILENAME = '.dockercfg'
 def expand_registry_url(hostname, insecure=False):
     if hostname.startswith('http:') or hostname.startswith('https:'):
         return hostname
-    if utils.ping('https://' + hostname + '/v1/_ping'):
+    if utils.ping_registry('https://' + hostname):
         return 'https://' + hostname
     elif insecure:
         return 'http://' + hostname

docker/utils/__init__.py

 from .utils import (
     compare_version, convert_port_bindings, convert_volume_binds,
-    mkbuildcontext, ping, tar, parse_repository_tag, parse_host,
+    mkbuildcontext, tar, parse_repository_tag, parse_host,
     kwargs_from_env, convert_filters, create_host_config,
-    create_container_config, parse_bytes
+    create_container_config, parse_bytes, ping_registry
 ) # flake8: noqa

docker/utils/utils.py

@@ -118,6 +118,10 @@ def compare_version(v1, v2):
         return 1
 
 
+def ping_registry(url):
+    return ping(url + '/v2/_ping') or ping(url + '/v1/_ping')
+
+
 def ping(url):
     try:
         res = requests.get(url, timeout=3)