Fix %post script failures in selinux-policy-*
    
    Since /etc/selinux/config is created in a %post script and execution
    order of post scripts cannot be ensured in this case, all commands in
    post have to be able to work without /etc/selinux/config.
    
    Also standalone execution of selinuxenabled in relabel macro would cause
    %post of all selinux-policy-* packages to fail in case selinux was
    disabled.
    
    Fixes:
       https://bugzilla.redhat.com/show_bug.cgi?id=1723940