Fix up sync-crls script and add to Dockerfile.

- Fix some python formatting and import issues
- Fix dockerfile to include sync-crls script
- Adjust sync-crls script to use paths and CLI tools available in the
  Docker container

atst/domain/authnid/crl/util.py

@@ -1,8 +1,8 @@
-import requests
 import re
 import os
+
 import pendulum
-from html.parser import HTMLParser
+import requests
 
 MODIFIED_TIME_BUFFER = 15 * 60