rgw/multisite: assign 'rgw_zone' to the exact section in ceph.conf

since the following commit:
  commit 1ac94c048f
  rgw: add support for multiple rgw instances on a single host

we have multi-instance rgw support on a single host and
the config section name of the rgw changed from
[client.rgw.$(hostname)] -> [client.rgw.$(hostname).rgwX]
when X is the sequence number: 0,1,2,...
So we should assign 'rgw_zone' item to the exact rgw instance
config section in ceph.conf

Signed-off-by: guihecheng <guihecheng@cmiot.chinamobile.com>

roles/ceph-rgw/tasks/multisite/main.yml

@@ -19,7 +19,10 @@
 - name: add zone to rgw stanza in ceph.conf
   ini_file:
     dest: "/etc/ceph/{{ cluster }}.conf"
-    section: "client.rgw.{{ ansible_hostname }}"
+    section: "client.rgw.{{ ansible_hostname }}.{{ item.instance_name }}"
     option: "rgw_zone"
     value: "{{ rgw_zone }}"
+  with_items: "{{ rgw_instances }}"
+  when:
+    - rgw_instances is defined
   notify: restart rgw