executor: fix admin show ddl jobs end time bug when job is not finished

[crazycs520]

Signed-off-by: crazycs crazycs520@gmail.com

What problem does this PR solve?

When DDL job doesn't finish, the END_TIME should be '' instead of 1970-01-01 08:00:00 +0800 CST.

Before this PR:

> admin show ddl jobs;
+--------+---------+------------+-----------+----------------------+-----------+----------+-----------+-----------------------------------+-----------------------------------+---------+
| JOB_ID | DB_NAME | TABLE_NAME | JOB_TYPE  | SCHEMA_STATE         | SCHEMA_ID | TABLE_ID | ROW_COUNT | START_TIME                        | END_TIME                          | STATE   |
+--------+---------+------------+-----------+----------------------+-----------+----------+-----------+-----------------------------------+-----------------------------------+---------+
| 57     | test    | t          | add index | write reorganization | 1         | 51       | 0         | 2020-02-12 11:07:01.817 +0800 CST | 1970-01-01 08:00:00 +0800 CST     | running |
| 58     | test    | t          | add index | none                 | 1         | 51       | 0         | 2020-02-12 11:07:02.972 +0800 CST | 1970-01-01 08:00:00 +0800 CST     | none    |
+--------+---------+------------+-----------+----------------------+-----------+----------+-----------+-----------------------------------+-----------------------------------+---------+

This PR:

+--------+---------+------------+-----------+--------------+-----------+----------+-----------+-----------------------------------+-----------------------------------+---------+
| JOB_ID | DB_NAME | TABLE_NAME | JOB_TYPE  | SCHEMA_STATE | SCHEMA_ID | TABLE_ID | ROW_COUNT | START_TIME                        | END_TIME                          | STATE   |
+--------+---------+------------+-----------+--------------+-----------+----------+-----------+-----------------------------------+-----------------------------------+---------+
| 59     | test    | t          | add index | delete only  | 1         | 51       | 0         | 2020-02-12 11:08:48.919 +0800 CST |                                   | running |
| 60     | test    | t          | add index | none         | 1         | 51       | 0         | 2020-02-12 11:08:49.919 +0800 CST |                                   | none    |
+--------+---------+------------+-----------+--------------+-----------+----------+-----------+-----------------------------------+-----------------------------------+---------+

What is changed and how it works?

Check List

Tests

• Unit test
• Manual test

Code changes

• Has exported function/method change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• Need to cherry-pick to the release branch

Release note

• Fix the END_TIME of admin show ddl jobs bug, when the DDL job not finish, the END_TIME should be "".

[tangenta]

LGTM

[zimulala]

LGTM

[sre-bot]

/run-all-tests

[bb7133]

LGTM