add support of DOCKER_API_VERSION

Signed-off-by: Mateusz Zakarczemny <m.zakarczemny+githyb@gmail.com>

docker/client.py

@@ -60,6 +60,11 @@ class DockerClient(object):
             A path to a directory containing TLS certificates to use when
             connecting to the Docker host.
 
+        .. envvar:: DOCKER_API_VERSION
+
+            A path to a directory containing TLS certificates to use when
+            connecting to the Docker host.
+
         Args:
             version (str): The version of the API to use. Set to ``auto`` to
                 automatically detect the server's version. Default: ``1.30``

docker/utils/utils.py

@@ -329,6 +329,8 @@ def kwargs_from_env(ssl_version=None, assert_hostname=None, environment=None):
         tls_verify = tls_verify is not None
     enable_tls = cert_path or tls_verify
 
+    docker_api_version = environment.get('DOCKER_API_VERSION')
+
     params = {}
 
     if host:
@@ -356,6 +358,8 @@ def kwargs_from_env(ssl_version=None, assert_hostname=None, environment=None):
         assert_hostname=assert_hostname,
     )
 
+    params['version'] = docker_api_version
+
     return params