Fix bug: count sql statement leak

[z7658329]

Fix bug: mysql count sql statement leak

fix #1626

[codecov]

Codecov Report

Merging #1640 (851a8b1) into master (cc509f9) will increase coverage by 0.41%.
The diff coverage is 40.00%.

@@             Coverage Diff              @@
##             master    #1640      +/-   ##
============================================
+ Coverage     62.83%   63.24%   +0.41%     
- Complexity     6737     6759      +22     
============================================
  Files           421      421              
  Lines         34645    34646       +1     
  Branches       4798     4798              
============================================
+ Hits          21770    21913     +143     
+ Misses        10606    10460     -146     
- Partials       2269     2273       +4     

Impacted Files	Coverage Δ
...om/baidu/hugegraph/backend/store/BackendEntry.java	72.22% <ø> (+2.77%)	⬆️
...aidu/hugegraph/backend/store/mysql/MysqlTable.java	0.00% <0.00%> (ø)
.../hugegraph/backend/store/rocksdb/RocksDBTable.java	70.99% <50.00%> (ø)
.../baidu/hugegraph/backend/query/ConditionQuery.java	86.11% <0.00%> (+0.27%)	⬆️
...c/main/java/com/baidu/hugegraph/task/HugeTask.java	72.30% <0.00%> (+0.30%)	⬆️
...a/com/baidu/hugegraph/backend/query/Condition.java	80.14% <0.00%> (+0.72%)	⬆️
.../backend/store/cassandra/CassandraSessionPool.java	57.14% <0.00%> (+1.02%)	⬆️
...egraph/backend/store/cassandra/CassandraShard.java	52.77% <0.00%> (+1.85%)	⬆️
.../backend/store/scylladb/ScyllaDBStoreProvider.java	94.59% <0.00%> (+94.59%)	⬆️
... and 2 more

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[z7658329]

与预期符合每次创建一个新连接，都会close该资源。

监控monitor代码：

[javeme]

LGTM!
we can specify the title like fix resultset leak for count query

[javeme]

nice, can you also fix rocksdb:

      try (BackendColumnIterator results = this.queryBy(session, query)) {
          if (results instanceof Countable) {
              return ((Countable) results).count();
          }
          return IteratorUtils.count(results);
      }