bootloader/zipl.py: update for zipl >= 2.25.0
    
    The output of the zipl tool has been changed in version 2.25.0 [1], thus
    adapt the line prefix in the anaconda check as well.
    
    [1] https://github.com/ibm-s390-linux/s390-tools/commit/f7d2339c6ad6c0adf1902a1a97a30b3168bc2c46
    
    Resolves: rhbz#2157916