add-build-sshkey: add centos/rhel-8 support

Assues we install libselinux on these platforms as otherwise Ansible
could choke with:

TASK [add-build-sshkey : Enable access via build key on all nodes]
"msg": "Aborting, target uses selinux but python bindings (libselinux-python) aren't installed!"

Change-Id: I91ec606b5b4e8dce7b71912fdc5890ac6aaf20ef

roles/add-build-sshkey/defaults/main.yaml

@@ -0,0 +1 @@
+system_packages: []

roles/add-build-sshkey/tasks/main.yaml

@@ -1,3 +1,14 @@
+- name: Include OS specific variables
+  include_vars: "{{ item }}"
+  failed_when: false
+  loop:
+      - "family-{{ ansible_os_family | lower }}.yml"
+      - "family-{{ ansible_os_family | lower }}-{{ ansible_distribution_major_version | lower }}.yml"
+      - "{{ ansible_distribution | lower }}.yml"
+      - "{{ ansible_distribution | lower }}-{{ ansible_distribution_major_version | lower }}.yml"
+      - "{{ ansible_distribution | lower }}-{{ ansible_distribution_version.split('.')[0:2] | join('-') | lower }}.yml"
+      - "{{ ansible_distribution | lower }}-{{ ansible_distribution_version.split('.')[0:3] | join('-') | lower }}.yml"
+
 - name: Check to see if ssh key was already created for this build
   stat:
     path: "{{ zuul_temp_ssh_key }}"
@@ -6,6 +17,11 @@
   run_once: true
   failed_when: false
 
+- name: Install required packages
+  when: system_packages
+  package:
+    name: "{{ system_packages }}"
+
 - name: Create a new key in workspace based on build UUID
   include: create-key-and-replace.yaml
   when:

roles/add-build-sshkey/vars/family-redhat-8.yml

@@ -0,0 +1,2 @@
+system_packages:
+  - python3-libselinux