code: @Override
      public ListRuleGroupsResult listRuleGroups(ListRuleGroupsRequest request) {
          request = beforeClientExecution(request);
          return executeListRuleGroups(request);
      }
docs: <p>
  Returns an array of <a>RuleGroup</a> objects.
  </p>
  
  @param listRuleGroupsRequest
  @return Result of the ListRuleGroups operation returned by the service.
  @throws WAFInternalErrorException
  The operation failed because of a system problem, even though the request was valid. Retry your request.
  @sample AWSWAFRegional.ListRuleGroups
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/waf-regional-2016-11-28/ListRuleGroups" target="_top">AWS
  API Documentation</a>