Update openjdk8 on stable branches
Follow-up to #8667
See also: #8853
On stable branches the OpenJDK/OpenJRE packages are still outdated and
have known security vulnerabilities.
Please backport them from “edge” to the stable/supported version(s) of
Alpine.
(from redmine: issue id 8978, created on 2018-06-10, closed on 2019-05-04)