cve-check: write the cve manifest to IMGDEPLOYDIR

When building an image cve_check_write_rootfs_manifest() would sometimes fail
with a FileNotFoundError when writing the manifest.cve due to the parent
directory (DEPLOY_DIR_IMAGE) not (yet) existing.

The image task will provide the manifest in the deploy directory afterwards,
so other recipes depending on the manifest being in DEPLOY_DIR_IMAGE should
continue to function properly.

Signed-off-by: Jermain Horsman <jermain.horsman@nedap.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>