[Fix] [IoT] Check scheduleReconnect() return value

[sklikowicz]

There is a bug in AWSIotMqttManager if auto reconnection is on (default).
If last reconnect attempt (10th by default) is successfully and there is following disconnect within the connection stability time (10 seconds by default) manager is not clearing reconnection counter so next reconnection is not scheduled and connection status is set to reconnect without checking returned value from the scheduleReconnect() method.

See:
setupCallbackForMqttClient()

if ((lastConnackTime + (connectionStabilityTime * MILLIS_IN_ONE_SECOND)) < getSystemTimeMs()) {
      resetReconnect(); // <--- will not call this method because stability time is not exceeded so the counter will not reset
 }
scheduleReconnect() ;// <--- this method will be called

scheduleReconnect()

if (maxAutoReconnectAttempts == -1 || autoReconnectsAttempted < maxAutoReconnectAttempts) { 
           {....} //<--- will not execute this code to start separete thread to reconnect because auto reconnnect counter was not reset and is higher then max
            return true;
        } else {
            return false; //<--- will execute this code and return false but setupCallbackForMqttClient() is not checking returned boolean and set connection status to reconnect before this called
        }