src/sysext: Use versioned names when logging extensions used for merge operation

src/sysext: Use versioned names when logging extensions used for merge operation

If this is not done, and there are two images, image_1.raw and image_2.raw under
an image.raw.v folder, then the log will say "Using extensions image" instead of
using "Using extensions image_2.raw" which is the desired behavior for v-picked extensions.