set password='xx' fails privilege check

[morgo]

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

I tried to change the password for a non-privileged user:

mysql> create user nobody;
^c
shell> mysql -unobody                                                                                                                                                                                 mysql> set password='acdc';
ERROR 1105 (HY000): privilege check fail
mysql> SET password=password('acdc');                                                                                                                                                                            ERROR 1105 (HY000): privilege check fail

2. What did you expect to see?

It should be possible to set your own password.

3. What did you see instead?

Error.

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?

MySQL [(none)]> SELECT tidb_version()\G                                                                                                                                                                                   *************************** 1. row ***************************
tidb_version(): Release Version: v2.1.0-rc.1-13-g1255973
Git Commit Hash: 1255973764f72575d71920b95fc0861d1677c6c5
Git Branch: master
UTC Build Time: 2018-08-28 07:35:57
GoVersion: go version go1.10.2 linux/amd64
Race Enabled: false
TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e
Check Table Before Drop: false
1 row in set (0.00 sec)