MSI-1438: Incompatibility with Sample Data

[nmalevanec]

Fixed Issues (if relevant)

1. Incompatibility with Sample Data #1438: Incompatibility with Sample Data

Manual testing scenarios 1

1. Install Magento with MSI and Sample Data.
2. Check, installation proceeds without any errors.

Manual testing scenarios 2

1. Install magento without MSI.
2. Navigate to admin area and create different types of products.
3. Export created products.
4. Install magento with MSI(single stock mode).
5. Import previously exported products.
6. Perform reindex, if needed.
7. Create order, invoice and shipment with imported products.
8. Check order, invoice and shipment created successfully.

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)