databases/mysql57-{client/server}: Update to 5.7.19
ChangeLog for this update: https://dev.mysql.com/doc/relnotes/mysql/5.7/en/news-5-7-19.html

PR: 220849
Reviewed by: mat (mentor)
Approved by: mat (mentor)
Sponsored by: Netzkommune GmbH
Differential Revision: https://reviews.freebsd.org/D11656