Update fonb-setup.py

i have updated the parser. At first its just removing the existing content with sed command and then echo-ing the simple lines, as discussed. 
As mentioned earlier as well, i couldn't replicate the exact bug, in normal conditions, thus it only malfunctions under abnormalities. The scenario, i imagined was when the key/value settings varies, the config parser was adding an '=' at the end. Since the parser is not working now, all it does is adds the sample lines in place.
what exactly have you done here? 
first sed will echo the result to standard output (stdout) so you need to write it as
sed '1,$d' self.config_file > self.config_file
second, sed is not defined in python, so you have to use os.system()
thrid, is your logic, all wrong. what you are doing is deleting all the lines. and what we want is to delete the OnHold, Conference and Hangup sections. you shouldn't delete all the lines. especially that it could hold other sections which is out of our scope. yet important to the client/user.
the task was to use sed to delete this section. not to delete all files. which could be done natively with python easily.