workaround for CloudStack API inconsistencies

Following the definition deleteIso command should return a response 'deleteisoresponse', but does actually return 'deleteisosresponse'. See https://github.com/apache/cloudstack/blob/master/api/src/org/apache/cloudstack/api/command/user/iso/DeleteIsoCmd.java#L41
Merge pull request #6 from resmo/fix/api_response_inconsistencies

workaround for CloudStack API inconsistencies