Vague error message for invalid url_key for category

[avdb]

Description

Problem: vague error message for invalid url_key for category
Example error message:
Invalid URL key

Solution: Use addFailedCategory() to add category to error message
Example error message:
1. Category " has not been created. Invalid URL key in row(s): 1

Fixed Issues (if relevant)

1. Product Import: Additional data: Invalid URL key #10697: Product Import: Additional data: Invalid URL key

Manual testing scenarios

1. System > Import > Products
2. Choose "Add/Update
3. Select a CSV file containing a "categories" column with a comma as the first character
4. Click Check Data then Import

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-cicd2]

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1 out of 3 committers have signed the CLA.

✅ avdb
❌ paliarush
❌ viktym