test if rtkit-daemon can do sys_nice in user namespaces
    
    SELinux prevents the rtkit-daemon process from setting nice value.
    I believe this access is harmless from security point-of-view and
    should be allowed. The TC is not able to reproduce the issue, but it
    looks for an appropriate SELinux policy rule.
    
    The TC covers BZ#1750024, BZ#1910507 and other duplicates.