image: Ensure manifests end with a newline

Manifests should end with a newline character but don't currently. This
is the easiest fix for now, the alternative would be a rewrite of the
internal code which is something to consider in due course.

[YOCTO #7427]

(From OE-Core rev: 98230d2d049c742c349f35b256b13afbc3d26235)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/image.bbclass

@@ -396,6 +396,7 @@ python write_image_manifest () {
     from oe.rootfs import image_list_installed_packages
     with open(d.getVar('IMAGE_MANIFEST', True), 'w+') as image_manifest:
         image_manifest.write(image_list_installed_packages(d, 'ver'))
+        image_manifest.write("\n")
 }
 
 # Can be use to create /etc/timestamp during image construction to give a reasonably