Ticket #48339 - Share nsslapd-threadnumber in the case nunc-stans is enabled, as well.
    
    Description:  When nunc-stans is enabled, instead of getting the
    thread number from the environment variable MAX_THREADS, use the
    value of config parameter nsslapd-threadnumber.
    
    https://fedorahosted.org/389/ticket/48339
    
    Reviewed by rmeggins@redhat.com (Thank you, Rich!!)
    
    (cherry picked from commit ab8ed9a5ebb0d15b55d7525ed1d5dbeebd8c7563)
    (cherry picked from commit a4c0a9eeba031b9304d63ca05d8b9fab9ebca1b2)