Refactor how clients access PCAP capture files. Fixes https://github.com/GNS3/gns3-gui/issues/2438.

* The PCAP file is directly accessed if controller and client are on the same host.
* The PCAP file is streamed from the compute server to the client with the controller as a proxy when the controller is remote for the client.

gns3server/web/route.py

@@ -248,9 +248,10 @@ class Route(object):
                 """
                 To avoid strange effect we prevent concurrency
                 between the same instance of the node
+                (excepting when streaming a PCAP file).
                 """
 
-                if "node_id" in request.match_info:
+                if "node_id" in request.match_info and not "pcap" in request.path:
                     node_id = request.match_info.get("node_id")
 
                     if "compute" in request.path: