Wait for comm layer to stop when gossip stops

Gossip's Stop() method stops underlying comm layer
asynchronously but doesn't wait for it to stop.
I simply changed it so that it now waits for it to stop
until the Stop() method exits.

Change-Id: I200a3d39408252e07c2b1fe6535515c3aea1e078
Signed-off-by: Yacov Manevich <yacovm@il.ibm.com>

gossip/gossip/gossip_impl.go

@@ -382,14 +382,20 @@ func (g *gossipServiceImpl) Stop() {
 	}
 	atomic.StoreInt32((&g.stopFlag), int32(1))
 	g.logger.Info("Stopping gossip")
-	go g.comm.Stop()
+	comWG := sync.WaitGroup{}
+	comWG.Add(1)
+	go func() {
+		defer comWG.Done()
+		g.comm.Stop()
+	}()
 	g.discAdapter.close()
-	go g.disc.Stop()
-	go g.pushPull.Stop()
+	g.disc.Stop()
+	g.pushPull.Stop()
 	g.toDieChan <- struct{}{}
 	g.emitter.Stop()
 	g.ChannelDeMultiplexer.Close()
 	g.stopSignal.Wait()
+	comWG.Wait()
 }
 
 func (g *gossipServiceImpl) UpdateMetadata(md []byte) {