When OpenFlow-capable switch goes down while RPC {add,remove,update}-flow is invoked, RESTCONF sockets are leaked

When OpenFlow-capable switch goes down while invoking RPC

-flow, RESTCONF socket are leaked, ending in CLOSE_WAIT state.

HOW TO REPRODUCE:
1. start OFP
2. feature:install odl-openflowplugin-flow-services-ui
3. connect a switch (OvS for instance)
4. run a script adding flow continuously (e.g. script attached)
5. disconnect the OvS

--> Observe result are:
a. the terminal window looping on the script is hanging on latest sent request
b. lsof -i :8181 or ss -nat | grep 8181 or whatever command to see open socket for port 8181
b. i. socket will be in ESTABLISHED state while a. is true
ii. stop the loop in the terminal --> the socket will be in CLOSE_WAIT
java 37558 adetalhouet 55u IPv6 0x2ef40e38b9d5893f 0t0 TCP localhost:8181->localhost:50860 (CLOSE_WAIT)

In a scaled environment, while provisioning switches, network can flap, thus failing those operations.

Even though nobody has complained about this, I believe this is a critical BUG as a fairly easy reproducible bug.