Control swupdate with signature verification enabled. For this to work swupdate must be compiled with signature verification enabled, otherwise the --key/--disable-verification flags are not present. We did not prepare to handle swupdate without verification. This script will still allow to install unverified images, by adding SWUPDATE_SIGNATURE_CHECK=0 in the reflash_request.conf, automatically added by reflash_rootfs -n flag. #17825