libselinux/setenforce: Drop and restore audit rules
    
    Some systems use default audit rule '-a never,task' which suppress audit
    messages. As a side effect, some tests fail as they don't find expected strings.
    
    Fixes:
    [   FAIL   ] :: Command 'ausearch --input-logs -m MAC_STATUS -i -ts 05/31/2018 13:04:51 | grep 'type=SYSCALL.*comm=setenforce'' (Expected 0, got 1)