Confluence Images Not Displayed in JIRA activity Stream

Copied to https://ecosystem.atlassian.net/browse/STRM-2137

The Activity Stream gadget does not render the images as it does not include the base url of Confluence. Since it does not have the base url prepended, the links are broken and images aren't rendered (it tries to resolve the image with the JIRA base url).
The following was the test (replicated locally with 5.1.1 JIRA and Confluence 4.2.11).

• Confluence and JIRA in two different machines
• Confluence using JIRA for user management (appears with different user management also)
• Activity stream gadget added to JIRA dashboard
• The images that are added to Confluence without resizing works correctly.
• The images which are resized in Confluence fails to show up in the Activity stream gadget (it does not have a base url prepended and it breaks).
• The same error happens for gallery too.