[IoT] Fix publish while reconnecting error reporting (#427)

* Problem: Publishing silently fails when client is reconnecting and
offline queues are disabled.
Fix: Allow application to handle republishing of failed messages OR
enable offline queues by throwing an exception under these conditions.

Author: sunilpalacherla

aws-android-sdk-iot/src/main/java/com/amazonaws/mobileconnectors/iot/AWSIotMqttManager.java

@@ -1262,6 +1262,8 @@ public void publishData(byte[] data, String topic, AWSIotMqttQos qos,
                             AWSIotMqttMessageDeliveryCallback.MessageDeliveryStatus.Fail,
                             userData);
                 }
+            } else {
+            	throw new AmazonClientException("Client is reconnecting and publishing from offline queue is disabled.");
             }
         } else {
             throw new AmazonClientException("Client is disconnected or not yet connected.");