1334: CreateOrderBackendTest rework to support MSI 'Reorder' button new behaviour.

[nmalevanec]

Description

Add shipment step to CreateOrderBackendTest in order to support "Reorder" button new behaviour with enabled MSI magento/inventory#680

Standard magento behaviour - "Reorder" button hides immediately after place order, but with MSI "Reorder" button hides only after shipment created, as MSI introduces additional property for product as 'salable quantity'. And after order placement, 'salable quantity' decreasing, not quantity itself(more about reservation mechanism here). Quantity decreasing only after shipment creation. So, in order to pass CreateOrderBackendTest with MSI, additional step with shipment creation should be added into test before assertions.

Fixed Issues (if relevant)

1. Fix Reorder Button functionality inventory#1162: Fix Reorder Button functionality

Manual testing scenarios

1. None.

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)

enterprise part: magento-engcom/magento2ee#161

[magento-cicd2]

All committers have signed the CLA.

[magento-engcom-team]

Hi @nmalevanec. Thank you for your contribution.
Changes from your Pull Request will be available with the upcoming 2.3.0 release.