Dissallow parallel pull of docker images

Fix #962

gns3server/compute/docker/docker_vm.py

@@ -24,7 +24,6 @@ import shutil
 import psutil
 import shlex
 import aiohttp
-import json
 import os
 
 from gns3server.utils.asyncio.telnet_server import AsyncioTelnetServer
@@ -767,26 +766,9 @@ class DockerVM(BaseNode):
         """
         Pull image from docker repository
         """
-        log.info("Pull %s from docker hub", image)
-        response = yield from self.manager.http_query("POST", "images/create", params={"fromImage": image}, timeout=None)
-        # The pull api will stream status via an HTTP JSON stream
-        content = ""
-        while True:
-            chunk = yield from response.content.read(1024)
-            if not chunk:
-                break
-            content += chunk.decode("utf-8")
-
-            try:
-                while True:
-                    content = content.lstrip(" \r\n\t")
-                    answer, index = json.JSONDecoder().raw_decode(content)
-                    if "progress" in answer:
-                        self.project.emit("log.info", {"message": "Pulling image {}:{}: {}".format(self._image, answer["id"], answer["progress"])})
-                    content = content[index:]
-            except ValueError:  # Partial JSON
-                pass
-        self.project.emit("log.info", {"message": "Success pulling image {}".format(self._image)})
+        def callback(msg):
+            self.project.emit("log.info", {"message": msg})
+        yield from self.manager.pull_image(image, progress_callback=callback)
 
     @asyncio.coroutine
     def _start_ubridge_capture(self, adapter_number, output_file):