add /api/tunnels/:id/status endpoint

Provides connected_sockets information for a tunnel.

lib/Client.js

@@ -12,6 +12,10 @@ class Client {
         this.debug = Debug('lt:Client');
     }
 
+    stats() {
+        return this.agent.stats();
+    }
+
     handleRequest(req, res) {
         this.debug('> %s', req.url);
         const opt = {

lib/TunnelAgent.js

@@ -39,6 +39,12 @@ class TunnelAgent extends Agent {
         this.closed = false;
     }
 
+    stats() {
+        return {
+            connectedSockets: this.connectedSockets,
+        };
+    }
+
     listen() {
         const server = this.server;
         if (this.started) {

lib/TunnelAgent.test.js

@@ -173,4 +173,11 @@ describe('TunnelAgent', () => {
         });
         assert.equal(err.message, 'foo');
     });
+
+    it('should return stats', async () => {
+        const agent = new TunnelAgent();
+        assert.deepEqual(agent.stats(), {
+            connectedSockets: 0,
+        });
+    });
 });