HTTP client should be able to get Device notification after subscription.
**

Implementation Details -
prerequisite - Notification stream should be enable in device. .

1. Added a new Device Notification Yang for Rest request which takes
input of Device mount point path
2. Added a DeviceNotificationListenerAdaptor which is get registered
in Device Notification server (on Mount point)
3. Created a dynamic Rest Notification SSE HTTP rest url (Response of 1st rest
call )
4. Updated Test tool for Notification

Sample -
1. Enable notification in device -
Post - /rests/operations/network-topology:network-topology/topology=topology-netconf/node=device_ios/yang-ext:mount/notifications:create-subscription
payload: 
{
  "input":

{     "stream": "NETCONF"   }

}

2. Create functionality to add/ register a listener in Netconf module for particular mount point of device 
Rest call -

POST - /rests/operations/odl-device-notification:subscribe-device-notification
Payload -
{
"input":

{ "path":"/network-topology:network-topology/topology[topology-id='topology-netconf']/node[node-id='device']" }

}

Response -
{
"odl-device-notification:output": {
"stream-path": "http://localhost:8181/rests/notif/device_ios?notificationType=device"
}
}
3. Add functionality for above rest call to start SSE Http connection to receive device notification for given mount point