Enable dnf integration tests on CentOS 8

Change:
We were only testing dnf on RHEL previously.
Test on CentOS 8 as well.

Test Plan:
Ran locally in docker.

Signed-off-by: Rick Elrod <rick@elrod.me>

test/integration/targets/dnf/tasks/dnfinstallroot.yml

@@ -11,7 +11,8 @@
 
 - name: Populate directory
   copy:
-    content: "{{ ansible_distribution_version }}\n"
+    # We need '8' for CentOS, but '8.x' for RHEL.
+    content: "{{ ansible_distribution_version|int if ansible_distribution != 'RedHat' else ansible_distribution_version }}\n"
     dest: "/{{ dnfroot.stdout }}/etc/dnf/vars/releasever"
 
 # This will drag in > 200 MB.

test/integration/targets/dnf/tasks/main.yml

@@ -21,15 +21,15 @@
 
 - include_tasks: dnf.yml
   when: (ansible_distribution == 'Fedora' and ansible_distribution_major_version is version('23', '>=')) or
-        (ansible_distribution == 'RedHat' and ansible_distribution_major_version is version('8', '>='))
+        (ansible_distribution in ['RedHat', 'CentOS'] and ansible_distribution_major_version is version('8', '>='))
 
 - include_tasks: repo.yml
   when: (ansible_distribution == 'Fedora' and ansible_distribution_major_version is version('23', '>=')) or
-        (ansible_distribution == 'RedHat' and ansible_distribution_major_version is version('8', '>='))
+        (ansible_distribution in ['RedHat', 'CentOS'] and ansible_distribution_major_version is version('8', '>='))
 
 - include_tasks: dnfinstallroot.yml
   when: (ansible_distribution == 'Fedora' and ansible_distribution_major_version is version('23', '>=')) or
-        (ansible_distribution == 'RedHat' and ansible_distribution_major_version is version('8', '>='))
+        (ansible_distribution in ['RedHat', 'CentOS'] and ansible_distribution_major_version is version('8', '>='))
 
 # Attempting to install a different RHEL release in a tmpdir doesn't work (rhel8 beta)
 - include_tasks: dnfreleasever.yml
@@ -39,4 +39,4 @@
 
 - include_tasks: modularity.yml
   when: (ansible_distribution == 'Fedora' and ansible_distribution_major_version is version('29', '>=')) or
-        (ansible_distribution == 'RedHat' and ansible_distribution_major_version is version('8', '>='))
+        (ansible_distribution in ['RedHat', 'CentOS'] and ansible_distribution_major_version is version('8', '>='))

test/integration/targets/dnf/vars/CentOS.yml

@@ -0,0 +1,2 @@
+astream_name: '@php:7.2/minimal'
+astream_name_no_stream: '@php/minimal'