Fix the incorrect container_facts

backport: pike

Closes-Bug: #1729564
Change-Id: If6db5fad1f23e0afaadcad97b4f37a13e34de9fa
(cherry picked from commit 994c80c7)

ansible/roles/ceph/tasks/precheck.yml

@@ -13,5 +13,5 @@
     timeout: 1
     state: stopped
   when:
-    - container_facts['ceph-rgw'] is not defined
+    - container_facts['ceph_rgw'] is not defined
     - inventory_hostname in groups['ceph-rgw']