playbook: Asser that firewalld is uninstalled

slapos.node package conflicts with firewalld, thus the latter one has to
be absent.

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

@@ -3,6 +3,10 @@
     apt: name=slapos-node state=present update_cache=yes cache_valid_time=3600
     when: ansible_os_family == "Debian"
 
+  - name: Uninstall firewalld on CentOS
+    yum: name=firewalld state=absent update_cache=yes
+    when: ansible_os_family == "RedHat"
+
   - name: Install re6stnet on CentOS
     yum: name=slapos.node state=present update_cache=yes
     when: ansible_os_family == "RedHat"