[Backport] 21842: don't cache absolute file paths in validator factory

[david-fuehr]

Original Pull Request

magento#21856

Description

This issue comes from Magento\Framework\Validator\Factory::_initializeConfigList where absolute file paths are cached. The actual file content is evaluated using the local file system.

The method is used in \Magento\Customer\Model\ResourceModel\Address::_validate, \Magento\Quote\Model\CustomerManagement::validateAddresses and \Magento\Customer\Model\ResourceModel\Customer::_validate and thus an error (The "/<abs_instance_path>/app/code/Magento/Eav/etc/validation.xml" file doesn't exist.) occurs whenever a customer, a customer_address or quote for a registered customer is saved.

Fixed Issues

1. Checkout error for registered customer with cache_id_prefix on multi server setup magento/magento2#21842: Checkout error for registered customer with cache_id_prefix on multi server setup

Manual testing scenarios

most realistic scenario

1. have a multi server setup with
   1. node backend (absolute instance dir: /var/www/backend/release/2019-02-28)
   2. node frontend-a (absolute instance dir: /var/www/frontend/release/2019-02-28)
   3. node frontend-b (absolute instance dir: /var/www/frontend/release/2019-03-01 - autospawned)
   4. node redis
   5. share cache for all Magento instances (identical id_prefix in cache section of env.php)
   6. [node mysql, ...]
2. clear cache on backend node
3. right after that save a customer or customer_address on the backend node (may be a cron job or similar)
4. place an order with a registered customer on one of the frontend-nodes
   1.expected: The success page is being shown

simplified repro steps

1. set up a regular instance
2. make sure that the id_prefix in env.php is defined

    'cache' => [
        'frontend' => [
            'default' => [
                'id_prefix' => '173_'
            ],
            'page_cache' => [
                'id_prefix' => '173_'
            ]
        ]
    ],

3. redis may be used, the issue can also be reproduced using file based caching
4. register a customer
5. place an order using this customer
6. move the instance directory to another path
7. update webserver configuration accordingly and restart
8. try to place an order with the same customer again
   1. expected: success page is being shown

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)