Use of emphemeral ports in iids causes breakage on reconnect

Using iids of the form ovsdb://<ip>:<port>/
Makes iids for ovs to controller connections change on each disconnect reconnect

Discussion:

a) Since passive (controller to ovs) connections require the user to decide on an iid before we connect to the switch (and thus know nothing but ip/port about what we are connecting to
b) Since config and oper iids should match for the same ovs
c) Therefore, we need to
i) Capture iids from config for passive connections
ii) 'Stamp' them into the external-ids for OpenVSwitch
iii) When we get the operational info from registercallbacks, we should either pick the 'stamp' from external-ids if it is present, or generate a unique iid ourselves.