Use /etc/ipa/nssdb to get nicknames of IPA certs installed in /etc/pki/nssdb
    
    Previously a list of nicknames was kept in /etc/pki/nssdb/ipa.txt. The file
    is removed now.
    
    https://fedorahosted.org/freeipa/ticket/3259
    
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>