[FIXED] LeafNode urls may be missing in INFO sent to LN connections

When a cluster of servers are having routes to each other, there
is a chance that the list of leafnode URLs maintained on each
server is not complete. This would result in LN servers connecting
to this cluster to not get the full list of possible URLs the
server could reconnect to.

Also fixed a DATA RACE that appeared when running the updated
TestLeafNodeInfoURLs test. Fixed the race and added specific
test that easily demonstrated the race: TestLeafNodeNoRaceGeneratingNonce

Signed-off-by: Ivan Kozlovic <ivan@synadia.com>

server/leafnode.go

@@ -507,9 +507,14 @@ func (s *Server) createLeafNode(conn net.Conn, remote *leafNodeCfg) *client {
 		c.leaf.remote = remote
 	}
 
+	var nonce [nonceLen]byte
+
 	// Grab server variables
 	s.mu.Lock()
 	info := s.copyLeafNodeInfo()
+	if !solicited {
+		s.generateNonce(nonce[:])
+	}
 	s.mu.Unlock()
 
 	// Grab lock
@@ -606,7 +611,7 @@ func (s *Server) createLeafNode(conn net.Conn, remote *leafNodeCfg) *client {
 		// Send our info to the other side.
 		// Remember the nonce we sent here for signatures, etc.
 		c.nonce = make([]byte, nonceLen)
-		s.generateNonce(c.nonce)
+		copy(c.nonce, nonce[:])
 		info.Nonce = string(c.nonce)
 		info.CID = c.cid
 		b, _ := json.Marshal(info)