Log RPMLOG_ERR level messages on actual errors in selinux plugin, doh.
    
    When there's an actual error, people will want to know without having
    to rerun in verbose mode. Such as in RhBug:1641631 where configured
    selinux policy differs from what is installed - the former message
    
        error: Plugin selinux: hook tsm_pre failed
    
    ...is not particularly helpful to anybody, whereas this actually provides
    some clues now:
    
        error: selabel_open: (/etc/selinux/ponies/contexts/files/file_contexts) No such file or directory
        error: Plugin selinux: hook tsm_pre failed