Bugfix: actually honor access_log class parameter on Debian Wheezy, Jessie, Stretch and sid.

Previously we would define two access_log directives: one through the nginx.conf
template (essentially equivalent to "access_log => distribution") and another
one via the nginx::access_log class. So not only we would log every access
twice, but we would log IPs even when the user told us not to, and even when the
user told us to disable access logging entirely.