Avoid 'non-zero return code' msg when ceph-ansible isn't installed

This patch uses 'rpm' command to know if the ceph-ansible package is installed
Whatever the return code, the command will return:

- 'package ceph-ansible is not installed'
or
- 'ceph-ansible-3.1.9-1.el7.noarch'

Adding '|| true' to the rpm command will get rid of the message
'exited with code: 1: non-zero return code' when ceph-ansible is not installed.

Change-Id: Ida251a81d0fe7b6904f43b4f78f2f4e26d93325a
Signed-off-by: Gael Chamoulaud <gchamoul@redhat.com>

validations/ceph-ansible-installed.yaml

@@ -9,14 +9,15 @@
         - pre-deployment
   tasks:
   - name: Check if ceph-ansible is installed
-    command: yum list installed ceph-ansible
+    shell: rpm -q ceph-ansible || true
     args:
       warn: no
-    ignore_errors: true
-    register: ceph_ansible_installed
     changed_when: False
+    ignore_errors: True
+    register: ceph_ansible_installed
+
   - name: Warn about missing ceph-ansible
     warn:
       msg: If planning to use Ceph, it is necessary to install the ceph-ansible on the undercloud
     when:
-      - ceph_ansible_installed is failed
+      - ceph_ansible_installed.stdout.find('is not installed') != -1