[Backport 2.1-develop] Correctly save Product Custom Option values

[JeroenVanLeusden]

Description

Backport of #13569

This occurred because the same value object is used for saving all values. After the save updateStoredData() is called and is used in prepareDataForUpdate().

magento2/lib/internal/Magento/Framework/Model/ResourceModel/Db/AbstractDb.php

Lines 718 to 733 in 3561b66

	protected function prepareDataForUpdate($object)
	{
	$data = $object->getData();
	foreach ($object->getStoredData() as $key => $value) {
	if (array_key_exists($key, $data) && $data[$key] === $value) {
	unset($data[$key]);
	}
	}
	$dataObject = clone $object;
	$dataObject->setData($data);
	$data = $this->_prepareDataForTable($dataObject, $this->getMainTable());
	unset($data[$this->getIdFieldName()]);
	unset($dataObject);
	return $data;
	}

Fixed Issues (if relevant)

1. Custom option values do not save correctly #5067: Custom option values do not save correctly

Manual testing scenarios

1. Install module ReachDigital_CustomOption.zip
2. An extra column as added to the Product Custom Options (http://cloud.h-o.nl/pP3N).
3. Uncheck all Changes Appearance checkboxes and save product.
4. Only the first checkbox is saved.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)