[TD-3639] <fix>: compare timestamp with datetime in python (#5940)

By this commit, It will close TD-3639.

It will not require test case to write *correct* datetime string to pass
a test case. One test could use seconds, milliseconds or microseconds to
check data.

That means the three tests are equivalent:

```python
.checkData(0, 0, "2020-01-01 00:00:00")
.checkData(0, 0, "2020-01-01 00:00:00.000")
.checkData(0, 0, "2020-01-01 00:00:00.000000")
```

tests/pytest/util/sql.py

@@ -136,6 +136,11 @@ class TDSql:
     def checkData(self, row, col, data):
         self.checkRowCol(row, col) 
         if self.queryResult[row][col] != data:            
+            if self.cursor.istype(col, "TIMESTAMP") and self.queryResult[row][col] == datetime.datetime.fromisoformat(data):
+                tdLog.info("sql:%s, row:%d col:%d data:%s == expect:%s" %
+                            (self.sql, row, col, self.queryResult[row][col], data))
+                return
+
             if str(self.queryResult[row][col]) == str(data):
                 tdLog.info("sql:%s, row:%d col:%d data:%s == expect:%s" %
                             (self.sql, row, col, self.queryResult[row][col], data))