busybox/check: disable module by default and check for busybox binary

modules.d/05busybox/check

@@ -1,2 +1,7 @@
 #!/bin/bash
-exit 0
+
+[[ $1 = -d ]] && exit 0
+
+type -P busybox >/dev/null || exit 1
+
+exit 255