20-grub-install: Restore default SELinux security contexts for BLS files
    
    The BLS files are copied from /lib/modules/$(uname -r)/bls.conf and this
    file has a SELinux label of "system_u:object_r:modules_object_t" like all
    the other files that are installed by the kernel package.
    
    But the files in the /boot directory are expected to have a SELinux label
    of "system_u:object_r:boot_t". For all the other files that are copied to
    /boot by the kernel-install script, the SELinux security contexts are
    restored to the default but that was missing for the BLS files.
    
    Resolves: rhbz#1726020
    
    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>