JCLOUDS-458: Addressing suggestions in PR-31

minor changes


The way jclouds handles this is by using custom [HttpErrorHandlers](https://github.com/jclouds/jclouds/blob/master/core/src/main/java/org/jclouds/http/HttpErrorHandler.java). You should write an error handler for this provider (you can take the [NovaErrorHandler](https://github.com/jclouds/jclouds/blob/master/apis/openstack-nova/src/main/java/org/jclouds/openstack/nova/v2_0/handlers/NovaErrorHandler.java) as an example) and configure it in the `GoogleCloudStorageHttpApiModule` similar to how the Nova one [is configured](https://github.com/jclouds/jclouds/blob/master/apis/openstack-nova/src/main/java/org/jclouds/openstack/nova/v2_0/config/NovaRestClientModule.java#L183-L188).

Then you can inspect the response code and the message in the handler and propagate an appropriate exception. Also consider changing the signature of the method to return `void` after implementing this.