isar-bootstrap-host: disable DISTRO_BOOTSTRAP_KEYS usage

isar-bootstrap-host only supports bootstrapping Debian root file
systems. Therefore deactivate any DISTRO_BOOTSTRAP_KEYS from other
distributions.

Signed-off-by: Claudius Heine <ch@denx.de>
[Maxim: rebased]
Signed-off-by: Maxim Yu. Osipov <mosipov@ilbers.de>

meta/recipes-core/isar-bootstrap/isar-bootstrap-host.bb

@@ -12,6 +12,8 @@ DEPLOY_ISAR_BOOTSTRAP = "${DEPLOY_DIR_BOOTSTRAP}/${HOST_DISTRO}-${HOST_ARCH}"
 ISAR_BOOTSTRAP_LOCK = "${DEPLOY_DIR_BOOTSTRAP}/${HOST_DISTRO}-${HOST_ARCH}.lock"
 
 require isar-bootstrap.inc
+# We only build debian host buildchroot environments
+DISTRO_BOOTSTRAP_KEYS = ""
 inherit isar-bootstrap-helper
 
 do_generate_keyrings[stamp-extra-info] = "${DISTRO}-${DISTRO_ARCH}"