[Chainquery] Upgrade from mysql TCP connections to direct .socket connection.

[Leopere]

Share socket from the mariadb container with the chainquery container via volumes then connect directly.

@nikooo777 mentioned in a slack message that we should be using mysql.socket via mysqldsn="lbry:PASSWORD@unix(/var/run/mysqld/mysqld.sock)/chainquery" in the Chainquery configurator start.sh

Using a direct socket connection will require testing but should vastly improve query speeds and security.

[EnigmaCurry]

It should support socket and TCP, as socket cannot be used in multi-host setups.

[nikooo777]

Why MariaDB btw? In production we use perconaDB.

Any considerable improvements?

Also if it's not easy to achieve we can stick to TCP, the speed improvements are minimal.

[EnigmaCurry]

@nikooo777 I've been testing with MySQL 5.7 (not MariaDB)

https://github.com/lbryio/lbry-docker/blame/master/contrib/systemd-cloud-init.md#L97

I can test with perconaDB, is there a specific version I should use?

[Leopere]

Why MariaDB btw? In production we use perconaDB.

Thanks for the reminder @nikooo777 I've opened a PR for a Percona swap. #69