[Backport] Fix $useCache for container child blocks

[gelanivishal]

Original Pull Request

#14029

Description

This is a follow-up from PR #4919.

When one would use getChildHtml() like the following to output a container uncached:
<?= $block->getChildHtml('category.products.list.product_meta', false); ?>
The container's child blocks would still be cached.

Fixed Issues (if relevant)

1. getChildHtml, $useCache and child containers #4919: getChildHtml, $useCache and child containers

Manual testing scenarios

1. Add a container to block category.products.list.
2. Add a custom template to the container and output something that should be different every time it gets rendered, like <?= rand() ?>.
3. Output the container in Magento/Catalog/templates/products/list.phtml using getChildHtml() and set $useCache to false.
4. The output is the same with each getChildHtml() of the container.

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)

[magento-engcom-team]

Hi @orlangur, thank you for the review.
ENGCOM-2153 has been created to process this Pull Request

[magento-engcom-team]

Hi @gelanivishal. Thank you for your contribution.
We will aim to release these changes as part of 2.1.15.
Please check the release notes for final confirmation.