Uses distribution based variables in app handlers

Based on PR review feedback, we are now using paths defined in the
variable vars files (based on the Ubuntu distribution value).

install_files/ansible-base/roles/app/handlers/main.yml

@@ -6,14 +6,7 @@
     state: restarted
 
 - name: reload iptables rules for xenial
-  shell: iptables-restore < /etc/network/iptables/rules_v4
-  when:
-    - ansible_distribution_release == 'xenial'
-
-- name: reload iptables rules for focal
-  shell: iptables-restore < /etc/iptables/rules.v4
-  when:
-    - ansible_distribution_release == 'focal'
+  shell: iptables-restore < "{{ iptables_v4_path }}"
 
 ## App/securedrop section
 - name: restart apache2

install_files/ansible-base/roles/app/tasks/main.yml

@@ -1,4 +1,6 @@
 ---
+- include_vars: "{{ ansible_distribution }}_{{ ansible_distribution_release }}.yml"
+
 - include: app_install_fpf_deb_pkgs.yml
   when: securedrop_app_install_from_repo
 

install_files/ansible-base/roles/app/vars/Ubuntu_focal.yml

@@ -0,0 +1,3 @@
+---
+
+iptables_v4_path: /etc/iptables/rules.v4

install_files/ansible-base/roles/app/vars/Ubuntu_xenial.yml

@@ -0,0 +1,3 @@
+---
+
+iptables_v4_path: /etc/network/iptables/rules_v4