code: @Override
      public DescribeAgentVersionsResult describeAgentVersions(DescribeAgentVersionsRequest request) {
          request = beforeClientExecution(request);
          return executeDescribeAgentVersions(request);
      }
docs: <p>
  Describes the available AWS OpsWorks Stacks agent versions. You must specify a stack ID or a configuration
  manager. <code>DescribeAgentVersions</code> returns a list of available agent versions for the specified stack or
  configuration manager.
  </p>
  
  @param describeAgentVersionsRequest
  @return Result of the DescribeAgentVersions operation returned by the service.
  @throws ValidationException
  Indicates that a request was not valid.
  @throws ResourceNotFoundException
  Indicates that a resource was not found.
  @sample AWSOpsWorks.DescribeAgentVersions
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/opsworks-2013-02-18/DescribeAgentVersions" target="_top">AWS
  API Documentation</a>