Improve error handling in create-firewall-data.py

[rgmz]

When running the scripts in the reports2/ directory, the create-firewall-data.py (and potentially others) doesn't properly handler failures from the IQ API.

$ cd reports2 && ./create-data.sh http://localhost:8070 admin admin123
applicationevaluations.json
applicationevaluations.csv
policyviolations.json
policyviolations.csv
componentsinquarantine.json
componentsinquarantine.csv
componentwaivers.json
componentwaivers.csv
./quarantine_data/autoreleased_from_quarantine_summary.json
Traceback (most recent call last):
  File "/Users/me/code/succes-metrics/successmetrics-84/reports2/create-firewall-data.py", line 249, in <module>
    main()
  File "/Users/me/code/succes-metrics/successmetrics-84/reports2/create-firewall-data.py", line 239, in main
    summary_report("autoreleased_from_quarantine_summary", "releaseQuarantine/summary")
  File "/Users/me/code/succes-metrics/successmetrics-84/reports2/create-firewall-data.py", line 66, in summary_report
    for key in data.keys():
AttributeError: 'str' object has no attribute 'keys'

This error is caused by the autoreleased_from_quarantine_summary.json file containing "Error fetching data" instead of the expected JSON.

$ cat reports2/quarantine_data/autoreleased_from_quarantine_summary.json
"Error fetching data"

When API requests fail, get_nexusiq_data returns "Error fetching data" (str); however, certain parts of the code expect that method to always return a dict:

iq-success-metrics2/releasefiles/reports2/create-firewall-data.py

Lines 65 to 67 in 60de16d

	line = []
	for key in data.keys():
	line.append(key)

iq-success-metrics2/releasefiles/reports2/create-firewall-data.py

Lines 36 to 39 in 60de16d

	if req.status_code == 200:
	res = req.json()
	else:
	res = "Error fetching data"