Correct exception message for error code 403

[miketran78727]

In jMeter test automation, I encountered a failure where error codes 400 and 403 were returned for DM request. 403 means that pending active DM request is in progress for one or more devices. 400 means incorrect request format.

Currently, 400 and 403 are mapped to Unexpected error:

2016/09/16 20:54:06 ERROR - com.ibm.iotf.load.test.dm.GatewayDeviceActions: initiateAction Thread 10: failed to initiate device action firmware/download HTTP error code: 403 Reason: Unexpected error code

2016/09/16 21:35:12 ERROR - com.ibm.iotf.load.test.dm.GatewayDeviceActions: initiateAction Thread 5: failed to initiate device action device/factory_reset HTTP error code: 400 Reason: Unexpected error code Response: null

[miketran78727]

@sathipal Could you please merge the pull request that fixes this issue? Thanks.