Fix wrong ceph mgr keyring name during creating

ceph mgr should use the each node name rather than the first node
inventory_hostname

Change-Id: Ib4530ee95b4201a941b836a3fbcbe27d2d03b06f

ansible/roles/ceph/tasks/start_mgrs.yml

 ---
 - name: Getting ceph mgr keyring
-  command: docker exec ceph_mon ceph auth get-or-create mgr.{{ inventory_hostname }} mon 'allow profile mgr' osd 'allow *' mds 'allow *'
+  command: docker exec ceph_mon ceph auth get-or-create mgr.{{ item }} mon 'allow profile mgr' osd 'allow *' mds 'allow *'
   register: ceph_mgr_keyring
   run_once: true
   delegate_to: "{{ groups['ceph-mon'][0] }}"