Fix a few bugs in CRL handling.

- Don't write a CRL to the cache if the response code is above 399. (We
  were getting HTML files as CRLs, d'oh).
- Fix a kwarg in the CRL logger (extras -> extra).
- Set Kubernetes clusters to log output as JSON.

k8s/azure/atst-envvars-configmap.yml

@@ -10,3 +10,4 @@ data:
   OVERRIDE_CONFIG_FULLPATH: /opt/atat/atst/atst-overrides.ini
   UWSGI_CONFIG_FULLPATH: /opt/atat/atst/uwsgi.ini
   CRL_STORAGE_PROVIDER: CLOUDFILES
+  LOG_JSON: "true"