Add tests for small/cover image import duplication

• Type: Task
• Status: Closed
• Priority: Minor
• Resolution: Completed
• Affects Version/s: None
• Fix Version/s: Master
• Component/s: Collaboration > Blogs
• Labels: None
• Epic/Theme:
  • Technical_Task
• Priority Level: Low
• Git Pull Request: https://github.com/sergiogonzalez/liferay-portal/pull/4483

Add tests to make sure small/cover images aren't freshly reimported after modifying the blogs entry content (but not changing the images).