Deleting a page displays "Done" even if the actual document delete failed

Steps to reproduce:

• create a test page with a large attachment (234MB)
• deleted the test page using More>Delete (see XWIKI-16782)

Result: the user gets the status "DONE" for the job even if it failed (the status.xml displays the full error)

Expected result: the status is failed with the proper error from status.xml (e.g. https://jira.xwiki.org/secure/attachment/37403/status.xml).