TLS support, with same env vars as docker client

Thanks to @jkingyens for the bulk of the work.

Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>

fig/cli/docker_client.py

@@ -0,0 +1,34 @@
+from docker import Client
+from docker import tls
+import ssl
+import os
+
+
+def docker_client():
+    """
+    Returns a docker-py client configured using environment variables
+    according to the same logic as the official Docker client.
+    """
+    cert_path = os.environ.get('DOCKER_CERT_PATH', '')
+    if cert_path == '':
+        cert_path = os.path.join(os.environ.get('HOME'), '.docker')
+
+    base_url = os.environ.get('DOCKER_HOST')
+    tls_config = None
+
+    if os.environ.get('DOCKER_TLS_VERIFY', '') != '':
+        parts = base_url.split('://', 1)
+        base_url = '%s://%s' % ('https', parts[1])
+
+        client_cert = (os.path.join(cert_path, 'cert.pem'), os.path.join(cert_path, 'key.pem'))
+        ca_cert = os.path.join(cert_path, 'ca.pem')
+
+        tls_config = tls.TLSConfig(
+            ssl_version=ssl.PROTOCOL_TLSv1,
+            verify=True,
+            assert_hostname=False,
+            client_cert=client_cert,
+            ca_cert=ca_cert,
+        )
+
+    return Client(base_url=base_url, tls=tls_config)