playbook: Fix distribution name to CentOS

playbook/roles/slapos-proxy/tasks/main.yml

@@ -16,11 +16,11 @@
 
   - name: Uninstall firewalld on CentOS
     yum: name=firewalld state=absent update_cache=yes
-    when: ansible_os_family == "RedHat"
+    when: ansible_distribution == "CentOS"
 
   - name: Install re6stnet on CentOS
     yum: name=slapos.node state=present update_cache=yes
-    when: ansible_os_family == "RedHat"
+    when: ansible_os_family == "CentOS"
 
   - name: Check if configuration exists already
     stat: path=/etc/opt/slapos/slapos.cfg