confctl is not functioning properly on cp2006/cp2012 after reimage (T208588):
```
07:59:17 ema@cp2006.codfw.wmnet:~
$ confctl select name=cp2006.codfw.wmnet get
CRITICAL:conftool:Could not load driver etcd: No module named 'dns'
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/conftool/backend.py", line 15, in __init__
exec(compile(open(driver_file).read(), driver_file, 'exec'), ctx)
File "/usr/lib/python3/dist-packages/conftool/drivers/etcd.py", line 4, in <module>
import etcd
File "/usr/lib/python3/dist-packages/etcd/__init__.py", line 2, in <module>
from .client import Client
File "/usr/lib/python3/dist-packages/etcd/client.py", line 21, in <module>
import dns.resolver
ImportError: No module named 'dns'
```
Installing python3-dns fixes the issue. A dependency on such package should probably be added to python3-etcd judging from the exception.