use set_server_option if possible

[ahorek]

Summary

original issue #31422 (since rails 5.2.0)

We loose all open transactions; Inside the original code, when inserting fixtures, a transaction is open. Multple delete statements are executed and finally the fixtures are inserted. The problem with this patch is that we need to open the transaction only after we reconnect to the DB otherwise reconnecting drops the open transaction which doesn't commit all delete statements and inserting fixtures doesn't work since we duplicated them (Primary key duplicate exception)...

it breaks https://github.com/DatabaseCleaner/database_cleaner transaction strategy

open a transaction
insert fixtures
run a test
rollback

the problem is that inserting fixtures reconnects to the db that drops all active transactions, so the next rollback won't work.

Other Information

I used brianmario/mysql2#943 for this purpose, but it's available only in mysql2 0.5.0+. There's a fallback to the previous (current) behaviour, but it won't fix the bug.
I added an additional workaround, if you set up Mysql2::Client::MULTI_STATEMENTS in a database config manually, it won't require reconnect. This way it will work even with previous versions of mysql2 gem.

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[ahorek]

I think that this should be backported to 5.2.x because it's a regression between 5.1.6 -> 5.2.
Transaction strategy is the fastest option for testing and now it fails without any error (mysql only). The transaction is just dropped silently.
Unfortunatelly this can't be fixed if mysql2 gem 4.x is used. Maybe this limitation should be documented somewhere?