Make CephConfigOverrides append to ceph.conf[global]

Previously it was mistakenly replacing the contents because we
do not do deep merge.

Change-Id: I145feb0208f135da7c71694ebcecd937244d66b1
Closes-Bug: #1719919
(cherry picked from commit 17416dcfc5)

docker/services/ceph-ansible/ceph-base.yaml

@@ -272,9 +272,9 @@ outputs:
           keys: *openstack_keys
           pools: []
           ceph_conf_overrides:
-            map_merge:
-              - global:
-                  osd_pool_default_size: {get_param: CephPoolDefaultSize}
+            global:
+              map_merge:
+                - osd_pool_default_size: {get_param: CephPoolDefaultSize}
                   osd_pool_default_pg_num: {get_param: CephPoolDefaultPgNum}
                   osd_pool_default_pgp_num: {get_param: CephPoolDefaultPgNum}
                   rgw_keystone_api_version: 3
@@ -285,7 +285,7 @@ outputs:
                   rgw_keystone_admin_user: swift
                   rgw_keystone_admin_password: {get_param: SwiftPassword}
                   rgw_s3_auth_use_keystone: 'true'
-              - {get_param: CephConfigOverrides}
+                - {get_param: CephConfigOverrides}
           ntp_service_enabled: false
           generate_fsid: false
           ip_version: