Fix tests for Debian Stretch

- nagios is not available
- curl can use HTTP2 (headers are lowercase)
- bypass tests when htpasswd is empty (bypass issue #28)

tests/includes/post_Debian.yml

@@ -1,11 +1,19 @@
 ---
 
-- name: APT | Install web apps
-  apt: pkg={{ item }} state=present install_recommends=no
+- name: APT | Install webapps
+  apt:
+    pkg: "{{ item }}"
+    state: present
+    install_recommends: no
   with_items:
     - backuppc
-    - nagios3
 #    - owncloud
 
+- name: APT | Install nagios3 (only on old Debian releases)
+  apt:
+    pkg: nagios3
+    state: present
+  when: ansible_distribution_major_version < 9
+
 - name: SERVICE | Ensure backuppc is started
   service: name=backuppc state=started