RESPONDERS: Make the fd_limit setting configurable
    
    This code will now attempt first to see if it has privilege to set
    the value as specified, and if not it will fall back to the
    previous behavior. So on systems with the CAP_SYS_RESOURCE
    capability granted to SSSD, it will be able to ignore the
    limits.conf hard limit.
    
    https://fedorahosted.org/sssd/ticket/1197