ovs-vsctl add-port optimization

[Alexandros Soumplis]

Trying to debug an issue with openvswitch recofngiuration hang, i ended up looking the code (I am in no way a developer) of the charm and noticed that in contrib/network/ovs/__init__.py the function add_bridge_port() executes a command similar to this:

ovs-vsctl -- --may-exist add-port br-ex-517 bond0.517

While this is expected to work fine, if there are many ports it might require a significant amount of time. According to openvswitch FAQ ( http://docs.openvswitch.org/en/latest/faq/issues/ search for "How can I do it faster" ) it is much more efficient to add all ports in one command.