Previous version add bugs that were not properly using the _api_key.
It also enforced to provide PANOS_USER and PANOS_PASSWORD which can be very constraining.
PANOS_KEY now has precedence. If not provided, the script falls back to PANOS_USER and PANOS_PASSWORD.
If the random dns challenge string happens to contain 'id',
the parsing method passed a broken, mingled mix of the
record's data and id field, instead of just the id. As a result,
deleting the TXT record failed. We now specifically look for
'"id":', which cannot appear as part of the challenge string.