privilege: fix atomic problem of DROP ROLE

[imtbkcat]

What problem does this PR solve?

TiDB has atomic problem at DROP ROLE, which can reproduce like this:

mysql root@127.0.0.1:test> select user, host from mysql.user where user in ('r1', 'r2', 'r3', 'r4');
+------+------+
| user | host |
+------+------+
0 rows in set
Time: 0.016s
mysql root@127.0.0.1:test> create role r2;
Query OK, 0 rows affected
Time: 0.004s
mysql root@127.0.0.1:test> create role r1, r2, r3
(1396, "Operation CREATE USER failed for 'r2'@'%'")
mysql root@127.0.0.1:test> select user, host from mysql.user where user in ('r1', 'r2', 'r3', 'r4');
+------+------+
| user | host |
+------+------+
| r2   | %    |
+------+------+
1 row in set
Time: 0.015s
mysql root@127.0.0.1:test> drop role 'r1', 'r2', 'r3';
(1396, 'Operation DROP USER failed for r1@%,r3@%')
mysql root@127.0.0.1:test> select user, host from mysql.user where user in ('r1', 'r2', 'r3', 'r4');
+------+------+
| user | host |
+------+------+
0 rows in set
Time: 0.012s
mysql root@127.0.0.1:test>

The problem was cause by error logic in DROP ROLE, which doesn't break loop when error occur.

What is changed and how it works?

Break the loop when drop user/role failed.

Check List

Tests

• Unit test

Code changes

• None

Side effects

• Increased code complexity

Related changes

• Need to cherry-pick to the release branch

Release note

• fix atomic problem of DROP ROLE

[imtbkcat]

/run-all-tests

[imtbkcat]

/run-all-tests tidb-test=pr/966

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@2cb5eb6). Click here to learn what that means.
The diff coverage is 31.0344%.

@@             Coverage Diff             @@
##             master     #14090   +/-   ##
===========================================
  Coverage          ?   80.1725%           
===========================================
  Files             ?        483           
  Lines             ?     121473           
  Branches          ?          0           
===========================================
  Hits              ?      97388           
  Misses            ?      16326           
  Partials          ?       7759

[imtbkcat]

/run-all-tests tidb-test=pr/966

[jackysp]

LGTM

[tiancaiamao]

LGTM

[jackysp]

/merge

[sre-bot]

/run-all-tests

[sre-bot]

@imtbkcat merge failed.

[jackysp]

/merge

[sre-bot]

/run-all-tests

[zyxbest]

/rebuild

[zyxbest]

/build

[zyxbest]

/merge

[sre-bot]

/run-all-tests

[sre-bot]

cherry pick to release-3.0 failed