定时保存snapshot到DB的逻辑中，schema名称获取错误，在有配置canal.instance.filter.regex时，由于对应的table无法被匹配中，导致compareTableMetaDbAndMemory方法不被执行 (#3693)

* 避免重复订阅zk变更状态

* Update DatabaseTableMeta.java

获取schema的名称

* Update CanalController.java

Author: happyrita

parse/src/main/java/com/alibaba/otter/canal/parse/inbound/mysql/tsdb/DatabaseTableMeta.java

@@ -301,7 +301,7 @@ private boolean applySnapshotToDB(EntryPosition position, boolean init) {
         boolean compareAll = true;
         for (Schema schema : tmpMemoryTableMeta.getRepository().getSchemas()) {
             for (String table : schema.showTables()) {
-                String fullName = schema + "." + table;
+                String fullName = schema.getName() + "." + table;
                 if (blackFilter == null || !blackFilter.filter(fullName)) {
                     if (filter == null || filter.filter(fullName)) {
                         // issue : https://github.com/alibaba/canal/issues/1168