worker: generate index flavor automatically by querying version info from DB

[lichunzhu]

What problem does this PR solve?

Now, we need to set flavor for DM-worker manually, but it may be set incorrectly.

What is changed and how it works?

use dbutil.ShowVersion and check.IsMariaDB from tidb-tools to detect upstream MySQL/MariaDB server type and set flavor automatically.

Check List

Tests

• Unit test
• Integration test

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation
• Need to be included in the release note

[lichunzhu]

/run-all-tests

[codecov]

Codecov Report

Merging #323 into master will increase coverage by 0.0254%.
The diff coverage is 53.125%.

@@               Coverage Diff                @@
##             master       #323        +/-   ##
================================================
+ Coverage   59.8923%   59.9177%   +0.0254%     
================================================
  Files           135        135                
  Lines         15047      15079        +32     
================================================
+ Hits           9012       9035        +23     
- Misses         5159       5163         +4     
- Partials        876        881         +5

[csuzhangxc]

@lichunzhu I found version_comment | (Ubuntu) in https://stackoverflow.com/questions/8987679/how-to-retrieve-the-current-version-of-a-mysql-database/8987742#8987742.

Can this (version, https://github.com/pingcap/tidb-tools/blob/3b04f08f9aa2a27d527aa9a5695663940b211fb2/pkg/check/mysql_server.go#L75) work?

[lichunzhu]

@csuzhangxc It works if we suppose customers only use mariaDB and mysql.
When we run select version seperately in mysql and mariaDB, mysql might be like:

+------------+
| @@version  |
+------------+
| 5.7.26-log |
+------------+

mariaDB might be like:

+--------------------------------------+
| @@version                            |
+--------------------------------------+
| 10.4.8-MariaDB-1:10.4.8+maria~bionic |
+--------------------------------------+

If there is a kind of database which supports select @@version command but is not neither mysql nor mariaDB, it would be judged as mysql.

[csuzhangxc]

If there is a kind of database which supports select @@version command but is not neither mysql nor mariaDB, it would be judged as mysql.

I think it's fine now, if neither mysql nor mariadb, it will fail later.

[lichunzhu]

So shall we change select @@version_comment to select @@version and use IsMariaDB?

[csuzhangxc]

So shall we change select @@version_comment to select @@version and use IsMariaDB?

I think to change to version it better. @WangXiangUSTC what's your opinion?

[csuzhangxc]

rest LGTM

[WangXiangUSTC]

LGTM

[csuzhangxc]

LGTM

[sre-bot]

cherry pick to release-1.0 failed