Merge pull request #2 from limed/master

Update Makefile
fix config loqding
Merge branch 'master' of github.com:mozilla-it/duo_openvpn
set config to None
I don't know.
Fix cfg variable.
improve logging when username is missing
[SECURITY] disable logging in with duopush and a user specified username
user specified usernames only work if using LDAP auth
This was previously done through a bash script which wasnt bundled.
Merge pull request #3 from limed/master

Update Makefile
check control file is present, else warn
use correct control file name
open control file for writing