The fix for CVE-2024-47211 results in image checksum being required in
all cases. However there is no requirement for checksums in
file:// based images.
This change checks for this situation. When checksum is missing for
file:// based image_source it is now calculated on-the-fly.
Change-Id: Ib2fd5ddcbee9a9d1c7e32770ec3d9b6cb20a2e2a
(cherry picked from commit b827c7bf72b02f88d8d899568bac1d2b07c371ab)