[QA] background scan does not scan external storage

[jnweiger]

Seen with files_antivirus-1.2.1-rc.1 (not a regression)

• activate background scanning.
• copy eicar.com.txt into the home folder of user admin and run occ file:scan --all
• The infected file appears in admin's home and can be downloaded. OKAYISH
• wait 20 Minutes. The infected file is now in the trashcan. OK
• set up a local SFTP external storage.
• copy eicar.com.txt into the SFTP storage and run occ file:scan --all
• The infected file appears in the storage and can be downloaded. OKAYISH
• wait 20 Minutes. The infected file is still there. BAD.