removed duplicate key

In review of this role it was discovered that we had a duplicate
key within a task. While this is acceptable in Ansible as it will
just use the last key found in a given task it is wrong and should
be removed. In later version of Ansible (2.1.0) a warning is printed
stating something similar to the following:

   [WARNING]: While constructing a mapping from xxx.yml, line xx,
     column xx, found a duplicate dict key (changed_when).  Using
     last defined value only. [WARNING]: While constructing a mapping
     from xxx.yml, line xx, column xx, found a duplicate dict key
     (changed_when).  Using last defined value only.

This chage cleans up the role by removing the duplication.

Change-Id: I164facafe810a47d0c922cc59687ba4f45da959a

playbooks/roles/ceph_client/tasks/ceph_auth.yml

@@ -80,7 +80,6 @@
 - name: Retrieve nova secret from cephcluster
   command: ceph auth get-key client.{{ nova_ceph_client }}
   when: inventory_hostname in groups.nova_compute
-  register: ceph_client_nova_secret
   always_run:   true
   changed_when: false
   failed_when:  false