Unhardcoding salt master name from cluster model.

It may differ from default and should refer to manageable variable

Prod-Related: PROD-29870

Change-Id: I6735e74a97d6beb3f6fa80327ef85fe27e2bf4f8
diff --git a/defaults/backup.yml b/defaults/backup.yml
index 1cff51b..8b54a2b 100644
--- a/defaults/backup.yml
+++ b/defaults/backup.yml
@@ -5,6 +5,6 @@
     backup_day_of_month: "*"
     backup_month: "*"
     backup_day_of_week: "*"
-    zookeeper_remote_backup_server: cfg01
-    cassandra_remote_backup_server: cfg01
+    zookeeper_remote_backup_server: ${_param:infra_config_hostname}
+    cassandra_remote_backup_server: ${_param:infra_config_hostname}
     xtrabackup_client_throttle: 0 # disabled