Python helper scripts: fix deprecation warning

[systemcrash]

DeprecationWarning: codecs.open() is deprecated. Use open() instead.

[jimklimov]

Thanks, this seems like it should work with pythons we care about in legacy OS practice (2.6+ and 3.x), but I'll let the multiplatform CI say if this change is OK ir needs if/else try/except etc. sort of handling.

[jimklimov]

So... more code is needed to make sure which python version we are running on (or just try/except for missing class properties or method signatures):

03:58:43  Regenerating Augeas ups.conf lens with 'python'...
03:58:43  Traceback (most recent call last):
03:58:43    File "./gen-nutupsconf-aug.py.in", line 82, in <module>
03:58:43      fd = open(filename, encoding='utf-8')
03:58:43  TypeError: 'encoding' is an invalid keyword argument for this function
03:58:43  + exit
script returned exit code 1

[jimklimov]

Will be extended and addressed by #3300, thanks.