exec: fix running with detach=True

Fixes #1271
Signed-off-by: Tomas Tomecek <ttomecek@redhat.com>

docker/api/exec_api.py

@@ -137,7 +137,8 @@ class ExecApiMixin(object):
             data=data,
             stream=True
         )
-
+        if detach:
+            return self._result(res)
         if socket:
             return self._get_raw_response_socket(res)
         return self._read_from_socket(res, stream)

tests/integration/api_exec_test.py

@@ -93,6 +93,21 @@ class ExecTest(BaseAPIIntegrationTest):
         data = read_exactly(socket, next_size)
         self.assertEqual(data.decode('utf-8'), line)
 
+    def test_exec_start_detached(self):
+        container = self.client.create_container(BUSYBOX, 'cat',
+                                                 detach=True, stdin_open=True)
+        container_id = container['Id']
+        self.client.start(container_id)
+        self.tmp_containers.append(container_id)
+
+        exec_id = self.client.exec_create(
+            container_id, ['printf', "asdqwe"])
+        self.assertIn('Id', exec_id)
+
+        response = self.client.exec_start(exec_id, detach=True)
+
+        self.assertEqual(response, "")
+
     def test_exec_inspect(self):
         container = self.client.create_container(BUSYBOX, 'cat',
                                                  detach=True, stdin_open=True)