websocket location should be in header when creating a resource

The work is being done here:
  https://jira.opendaylight.org/browse/NETCONF-676

which looks like a duplicate of:
  https://jira.opendaylight.org/browse/NETCONF-659

I think 676 might be covering a little more than 659, but at least for 659 it's easy to see
that the beirman GET on a notification subscription will have the location in the response
header:

https://logs.opendaylight.org/releng/vex-yul-odl-jenkins-1/netconf-csit-1node-userfeatures-all-aluminium/54/robot-plugin/log.html.gz#s1-s6-s1-t3-k4-k2

 {'Content-Length': '172', 'Content-Type': 'application/xml', 'Location': 'ws://10.30.170.68:8185/data-change-event-subscription/opendaylight-inventory:nodes/datastore=CONFIGURATION/scope=BASE'}

whereas in rfc8040 test, its not there:

https://logs.opendaylight.org/releng/vex-yul-odl-jenkins-1/netconf-csit-1node-userfeatures-rfc8040-all-aluminium/54/robot-plugin/log.html.gz#s1-s6-s1-t3-k4-k2

{'Content-Length': '178', 'Content-Type': 'application/xml'}