Evaluate use of "READ-COMMITTED" mode mysql setting.

[lliss]

We've been experiencing database deadlocks while running certain tasks.
Some docs seem to indicate that using READ-COMMITTED mode might alleviate these issues.
https://www.drupal.org/node/1952972
https://dev.mysql.com/doc/refman/5.7/en/set-transaction.html#isolevel_read-committed
https://groups.drupal.org/node/415883

We should be able to add:

transaction-isolation = READ-COMMITTED

in my.cnf under the [mysqld] section.

Try this out and see if everything still works.