Add a kernel-install plugin to execute hook scripts in /etc/kernel/
    
    The kernel hook scripts in /etc/kernel/postinst.d and /etc/kernel/prerm.d
    were executed by the new-kernel-pkg --rpmposttrans and --remove options.
    
    But with a BLS configuration the new-kernel-pkg script isn't executed and
    instead the kernel-install plugins are used. Add a kernel-install plugin
    that executes the hooks since packages like dkms and akmod make use of it.
    
    Resolves: rhbz#1696202
    
    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>