Fixes #13: Allow configuration of default_release parameter for apt installation.

defaults/main.yml

@@ -1,4 +1,7 @@
 ---
+# Used only for Debian/Ubuntu installation, as the -t option for apt.
+nginx_default_release: ""
+
 nginx_worker_processes: "1"
 nginx_worker_connections: "1024"
 

tasks/setup-Debian.yml

@@ -1,3 +1,6 @@
 ---
 - name: Ensure nginx is installed.
-  apt: pkg=nginx state=installed
+  apt:
+    pkg: nginx
+    state: installed
+    default_release: "{{ nginx_default_release }}"