new: [vps] make ``vps backup`` compatible with new ``cron`` containers

bin/vps

@@ -916,9 +916,25 @@ compose:get_cron_docker_cmd() {
     local cron_line cmd_line docker_cmd
     project_name=$(compose:project_name) || return 1
 
+    container=$(compose:service:containers "${project_name}" "cron") || {
+        err "Can't find service 'cron' in project ${project_name}."
+        return 1
+    }
+    if docker exec "$container" test -e /etc/cron.d/rsync-backup; then
         if ! cron_line=$(docker exec "${project_name}"_cron_1 cat /etc/cron.d/rsync-backup | grep "\* \* \*"); then
             err "Can't find cron_line in cron container."
-        echo "  Have you forgotten to run 'compose up' ?" >&2
+            return 1
+        fi
+    elif docker exec "$container" test -e /etc/crontabs/root; then
+        if ! cron_line=$(docker exec "$container" cat /etc/crontabs/root | grep " launch-rsync-backup " | grep "\* \* \*"); then
+            err "Can't find cron_line in cron container."
+            return 1
+        fi
+    else
+        err "Unrecognized cron container:"
+        echo "  Can't find neither:" >&2
+        echo "  - /etc/cron.d/rsync-backup for old-style cron services" >&2
+        echo "  - nor /etc/crontabs/root for new-style cron services." >&2
         return 1
     fi