Bring role up to spec (2.5+, Debian 9) and introduce LetsEncrypt support (#5)

* Bring role up to spec (2.5+) and introduce LetsEncrypt support
* Add Debian 9 support and fix script args chdir
* Use correct schema for travis and use command instead of script
* Make use of requirements.txt for build and fix syntax
* Got better at reading the docs now
* Minor improvements

tasks/prerequisites-Debian.yml

@@ -7,7 +7,9 @@
     state: present
   with_items:
   - "{{ directadmin_debian6_packages }}"
-  when: "ansible_distribution == 'Debian' and ansible_distribution_release == 'squeeze'"
+  when:
+  - ansible_distribution == 'Debian'
+  - ansible_distribution_release == 'squeeze'
 
 - name: Install dependencies for Debian 7 Wheezy
   apt:
@@ -17,7 +19,9 @@
     state: present
   with_items:
   - "{{ directadmin_debian7_packages }}"
-  when: "ansible_distribution == 'Debian' and ansible_distribution_release == 'wheezy'"
+  when:
+  - ansible_distribution == 'Debian'
+  - ansible_distribution_release == 'wheezy'
 
 - name: Install dependencies for Debian 8 Jessie
   apt:
@@ -26,5 +30,19 @@
     cache_valid_time: "{{ directadmin_cache_timeout }}"
     state: present
   with_items:
-  - "{{ directadmin_debian8_packages }}"
-  when: "ansible_distribution == 'Debian' and ansible_distribution_release == 'jessie'"
+  - "{{ directadmin_debian9_packages }}"
+  when:
+  - ansible_distribution == 'Debian'
+  - ansible_distribution_release == 'jessie'
+
+  - name: Install dependencies for Debian 9 Stretch
+    apt:
+      name: "{{ item }}"
+      update_cache: yes
+      cache_valid_time: "{{ directadmin_cache_timeout }}"
+      state: present
+    with_items:
+    - "{{ directadmin_debian8_packages }}"
+    when:
+    - ansible_distribution == 'Debian'
+    - ansible_distribution_release == 'jessie'