Drupal 8 Webform Schema errors

Problem:
--------
Trying to get a test to use a custom handler, defaultConfiguration()
in QuizFormHandler references a configuration setting called 'training_program'. 
In order for this to work properly during install, Drupal needs to know the schema
of any handlers that have configuration settings

Webform missing schema error
----------------------------
Drupal\Core\Config\Schema\SchemaIncompleteException : 
  Schema errors for webform.webform.test_quiz_section_1 with the following errors: 
    webform.webform.test_quiz_section_1:handlers.quiz_handler.settings.training_program missing schema

Solution:
---------
Create schema file which provides the configuration referenced in QuizFormHandler.php

1. Create file named quiz_form_handler.schema.yml in mymodule/config/schema
2. the top-level key needs to be webform.handler.quiz_form_handler (must match id provided in @WebformHandler annotation)
3. the rest of the file defines the configuration

quiz_form_handler.schema.yml:
-----------------------------
webform.handler.quiz_form_handler:
  type: mapping
  label: 'Quiz Handler'
  mapping:
    training_program:
      label: 'Training Program'
      type: integer

QuizFormHandler.php - annotation
--------------------------------
/**
 * Webform Quiz handler.
 *
 * @WebformHandler(
 
 *   id = "quiz_form_handler",  <-- this webform handler's id
 
 *   label = @Translation("Quiz Handler"),
 *   category = @Translation("Quiz"),
 *   description = @Translation("Validate Quiz submissions."),
 *   cardinality = \Drupal\webform\Plugin\WebformHandlerInterface::CARDINALITY_UNLIMITED,
 *   results = \Drupal\webform\Plugin\WebformHandlerInterface::RESULTS_PROCESSED,
 *   submission = \Drupal\webform\Plugin\WebformHandlerInterface::SUBMISSION_OPTIONAL,
 * )
 */