Fix docker console port lost during update

Fix https://github.com/GNS3/gns3-gui/issues/1026

gns3server/modules/docker/docker_vm.py

@@ -184,8 +184,11 @@ class DockerVM(BaseVM):
         """
         Destroy an recreate the container with the new settings
         """
+        # We need to save the console port and restore it
+        console = self.console
         yield from self.remove()
         yield from self.create()
+        self.console = console
 
     @asyncio.coroutine
     def start(self):