Install lsb-release on Debian distros if unavailable

Certain more-minimal Debian installations may not have
lsb-release installed, which makes the playbook fail.

We need lsb-release on Debian, so that ansible_lsb
could tell us if this is Debian or Raspbian.

roles/matrix-base/tasks/server_base/setup.yml

@@ -3,11 +3,26 @@
 - include_tasks: "{{ role_path }}/tasks/server_base/setup_centos.yml"
   when: ansible_distribution == 'CentOS'
 
-- include_tasks: "{{ role_path }}/tasks/server_base/setup_debian.yml"
-  when: (ansible_os_family == 'Debian') and (ansible_lsb.id != 'Raspbian') 
+- block:
+  # ansible_lsb is only available if lsb-release is installed.
+  - name: Ensure lsb-release installed
+    apt:
+      name:
+        - lsb-release
+      state: present
+      update_cache: yes
+    register: lsb_release_installation_result
 
-- include_tasks: "{{ role_path }}/tasks/server_base/setup_raspbian.yml"
-  when: (ansible_os_family == 'Debian') and (ansible_lsb.id == 'Raspbian') 
+  - name: Reread ansible_lsb facts if lsb-release got installed
+    setup: filter=ansible_lsb*
+    when: lsb_release_installation_result.changed
+
+  - include_tasks: "{{ role_path }}/tasks/server_base/setup_debian.yml"
+    when: (ansible_os_family == 'Debian') and (ansible_lsb.id != 'Raspbian')
+
+  - include_tasks: "{{ role_path }}/tasks/server_base/setup_raspbian.yml"
+    when: (ansible_os_family == 'Debian') and (ansible_lsb.id == 'Raspbian')
+  when: ansible_os_family == 'Debian'
 
 - include_tasks: "{{ role_path }}/tasks/server_base/setup_archlinux.yml"
   when: ansible_distribution == 'Archlinux'