Use real pg configuration instead of the "last clean" one for generating PG history

Basically fixes the bug introduced in 0.5.7 where an rebalance interrupted
by the monitor could result in forgetting objects moved to the new place

mon/mon.js

@@ -845,13 +845,19 @@ class Mon
                 pool_tree = pool_tree ? pool_tree.children : [];
                 pool_tree = LPOptimizer.flatten_tree(pool_tree, levels, pool_cfg.failure_domain, 'osd');
                 this.filter_osds_by_tags(osd_tree, pool_tree, pool_cfg.osd_tags);
-                const prev_pg_hash = (this.state.history.last_clean_pgs.items||{})[pool_id]
-                    || (this.state.config.pgs.items||{})[pool_id] || {};
-                const prev_pgs = [];
-                for (const pg in prev_pg_hash)
+                // These are for the purpose of building history.osd_sets
+                const real_prev_pgs = [];
+                for (const pg in ((this.state.config.pgs.items||{})[pool_id]||{}))
                 {
-                    prev_pgs[pg-1] = prev_pg_hash[pg].osd_set;
+                    real_prev_pgs[pg-1] = this.state.config.pgs.items[pool_id][pg].osd_set;
                 }
+                // And these are for the purpose of minimizing data movement
+                let prev_pgs = [];
+                for (const pg in ((this.state.history.last_clean_pgs.items||{})[pool_id]||{}))
+                {
+                    prev_pgs[pg-1] = this.state.history.last_clean_pgs.items[pool_id][pg].osd_set;
+                }
+                prev_pgs = JSON.parse(JSON.stringify(prev_pgs.length ? prev_pgs : real_prev_pgs));
                 const pg_history = [];
                 const old_pg_count = prev_pgs.length;
                 let optimize_result;
@@ -909,7 +915,7 @@ class Mon
                     } });
                 }
                 LPOptimizer.print_change_stats(optimize_result);
-                this.save_new_pgs_txn(etcd_request, pool_id, up_osds, prev_pgs, optimize_result.int_pgs, pg_history);
+                this.save_new_pgs_txn(etcd_request, pool_id, up_osds, real_prev_pgs, optimize_result.int_pgs, pg_history);
             }
             this.state.config.pgs.hash = tree_hash;
             await this.save_pg_config(etcd_request);