fedora-kata-osbuilder.sh: Support 'regenerate' option
    
    This skips the host kernel symlink check, so we will regenerate the
    appliance for the current installer kernel.
    
    Use this subcommand at RPM post time, so an update or reinstall of the
    package will refresh the current appliance.
    
    Also wire it up to kata-osbuilder-generate.service service 'reload'
    
    Signed-off-by: Cole Robinson <crobinso@redhat.com>