code: @Override
      public DescribeSeverityLevelsResult describeSeverityLevels(DescribeSeverityLevelsRequest request) {
          request = beforeClientExecution(request);
          return executeDescribeSeverityLevels(request);
      }
docs: <p>
  Returns the list of severity levels that you can assign to an AWS Support case. The severity level for a case is
  also a field in the <a>CaseDetails</a> data type included in any <a>CreateCase</a> request.
  </p>
  
  @param describeSeverityLevelsRequest
  @return Result of the DescribeSeverityLevels operation returned by the service.
  @throws InternalServerErrorException
  An internal server error occurred.
  @sample AWSSupport.DescribeSeverityLevels
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/support-2013-04-15/DescribeSeverityLevels" target="_top">AWS
  API Documentation</a>