Adds a test environment for CentOS 8.
Change-Id: I0aee89c84a443055bb052164469cc2a5f841aa72
Signed-off-by: Thanh Ha <zxiiro@gmail.com>
 platforms:
   - name: centos7
     image: centos:7
+  - name: centos8
+    image: centos:8
   - name: ubuntu1604
     image: ubuntu:16.04
   - name: ubuntu1804
 
       become: true
     - name: Install EPEL repository
       yum:
-        name: https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
+        name: https://dl.fedoraproject.org/pub/epel/epel-release-latest-{{ ansible_distribution_major_version }}.noarch.rpm
         state: present
       when: ansible_os_family == 'RedHat'
       become: true