Fixes 6621 etcd backup directory is consuming much rootfs disk space (#6836)

* added an ansible var to manage retention of etcd backups

* refactord ls/grep into find in etcd backup removal command

roles/etcd/defaults/main.yml

@@ -9,6 +9,8 @@ etcd_events_cluster_enabled: false
 etcd_backup_prefix: "/var/backups"
 etcd_data_dir: "/var/lib/etcd"
 
+# Number of etcd backups to retain. Set to a value < 0 to retain all backups
+etcd_backup_retention_count: -1
 
 etcd_config_dir: /etc/ssl/etcd
 etcd_cert_dir: "{{ etcd_config_dir }}/ssl"