bug 8671 same client notified multiple times

bug 8671 same client notified multiple times

only leader node will initialize topology
each node listens for topology creation/add event
once it receives the add event opens the ovsdb port to clients
Now we are absolutely sure that topology node can be created for the
new incoming connections.

when a new node joins/leaves the cluster , the leader node
will reinit the topology which is a no op event

Change-Id: I45c319195f593d8bd99b19f07f5568492cf9077f
Signed-off-by: K.V Suneelu Verma <k.v.suneelu.verma@ericsson.com>