Do not fail even if dnf cleanup fails

Since ansible 2.8, dnf module fails if repository name contains '*' and
no repogitory which matches the expression detected.
This patch makes current playbook avoid errors during dnf cleanup task,
so that the tasks can pass even if there is no dnf repositories
configured.

Conflicts:
	playbooks/prepare-node-common.yaml

Change-Id: Ie0a7e6455e68b387a9d392fc1fc8c970da86cddf
(cherry picked from commit 7e40c8c875)

playbooks/prepare-node-common.yaml

@@ -34,6 +34,7 @@
         name: "{{ item }}"
         state: absent
       become: true
+      ignore_errors: true
       when:
         - ansible_os_family == 'RedHat'
         - ansible_distribution != "Fedora"