Gracefully handle importing certificates with missing data (#674)

* fixing index out of range issue

* catching exceptions is common values aren't set

* fixing lint errors

* fixing unrelated lint/import error

lemur/certificates/verify.py

@@ -7,6 +7,7 @@
 """
 import requests
 import subprocess
+from requests.exceptions import ConnectionError
 from cryptography import x509
 from cryptography.hazmat.backends import default_backend