Update default keepalive to 5 minutes, add reset on ping fail to CC3k sketch.

Adafruit_MQTT.h

@@ -62,8 +62,8 @@
 #define PUBLISH_TIMEOUT_MS 500
 #define PING_TIMEOUT_MS 500
 
-// Adjust as necessary, in seconds
-#define MQTT_CONN_KEEPALIVE 15
+// Adjust as necessary, in seconds.  Default to 5 minutes.
+#define MQTT_CONN_KEEPALIVE 300
 
 // Largest full packet we're able to send.
 // Need to be able to store at least ~90 chars for a connect packet with full 

examples/mqtt_cc3k/mqtt_cc3k.ino

@@ -129,8 +129,10 @@ void loop() {
   // Try to ping the MQTT server
   /*
   if (! mqtt.ping(3) ) {
-    // MQTT pings failed, lets reconnect
-    Serial.println("Ping fail!");
+    // MQTT pings failed, let's reconnect by forcing a watchdog reset.
+    Serial.println("Ping fail! Resetting...");
+    Watchdog.enable(8000);
+    delay(10000);
   }
   */