Bug 370:catch and ignore when exceptions are raised while retreiving reverse domain records

 catch and ignore when exceptions are raised while retreiving reverse domain records this closes issue 370 
It's generally best to capture the most specific exception possible. In this case, there's the SoftLayer.SoftLayerError, which all other SL client exceptions are derived from: https://github.com/softlayer/softlayer-python/blob/master/SoftLayer/exceptions.py#L11