Use information from the certificate subject when setting the NSS nickname.
    
    There were a few places in the code where certs were loaded from a
    PKCS#7 file or a chain in a PEM file. The certificates got very
    generic nicknames.
    
    We can instead pull the subject from the certificate and use that as
    the nickname.
    
    https://fedorahosted.org/freeipa/ticket/1141