RHCS4 - Ceph ansible-playbook fails with 'ansible.vars.hostvars.HostVarsVars object' has no attribute 'rgw_instances_host'

Issue

Various Ceph ansible-playbooks will fail during facts gathering with:

TASK [ceph-facts : set_fact rgw_instances_all] ****
fatal: [magna055]: FAILED! => 
  msg: |-
    The task includes an option with an undefined variable. The error was: 'ansible.vars.hostvars.HostVarsVars object' has no attribute 'rgw_instances_host'

    The error appears to be in '/usr/share/ceph-ansible/roles/ceph-facts/tasks/set_radosgw_address.yml': line 77, column 3, but may
    be elsewhere in the file depending on the exact syntax problem.

    The offending line appears to be:


    - name: set_fact rgw_instances_all
      ^ here