Fix an issue when the DNS AD referal is in the path.
An Exception is raised, with the following stacktrace::
Traceback (most recent call last):
File "/www/lemur/lemur/auth/views.py", line 317, in post
user = ldap_principal.authenticate()
File "/www/lemur/lemur/auth/ldap.py", line 147, in authenticate
self._bind()
File "/www/lemur/lemur/auth/ldap.py", line 216, in _bind
self.ldap_groups.append(values["cn"][0].decode("ascii"))
TypeError: list indices must be integers or slices, not str
This is issue is trigerred by some extra rows that referrences
the DNS subtree::
['ldaps://DomainDnsZones.xxxx']
Limiting the extraction to the expected dicts fix this issue.
57208fe198