bin/untangle-https-backup: disable configuration file interpolation.

bin/untangle-https-backup: disable configuration file interpolation.

It was bound to happen: somebody changed their password to something
with a percent sign in it, and it broke the secret ConfigParser
interpolation that I didn't know existed. Nobody is interpolating
usernames or version numbers into their password fields (if you are;
see you in hell), so passing interpolation=None to our ConfigParser
instantiation should fix the issue.