Add /opt/java/openjdk as a potential Java source for jenkins/ssh-agent AdoptOpenJDK Alpine images

[oleg-nenashev]

Jus a minor tweak which helps the instance to discover Java when using the new AdoptOpenJDK packages for alpine. https://github.com/jenkinsci/docker-ssh-agent/blob/master/8/alpine/Dockerfile

See JENKINS-XXXXX.

Submitter checklist

• JIRA issue is well described
• Appropriate autotests or explanation to why this change has no tests

[MarkEWaite]

Confirmed that /opt/java/openjdk/bin/java is installed in jenkins/ssh-agent:3.0.0-alpine and reports Java version 1.8.0_262.

[kuisathaverat]

we cannot add all the path that exists n the world, the JVM should be on the PATH because is a requirement, if not you should pass the java path setting. Here we are trying to resolve an issue with paths in the Docker image with a sticker in another place. I've deprecated the java check class a few days a do and I will remove it in a year or so.
The proper solution for the Docker images is to set the environment correctly, I have done it for months in my test environments https://github.com/kuisathaverat/jenkins-issues/blob/master/kex-algorithms/ssh-agent-dsa/Dockerfile#L18

[kuisathaverat]

The issue is in the Docker image not in the plugin and the solution is to fix the Docker image by fixing jenkinsci/docker-ssh-agent#33, you can do it by adding Java to the Path or by creating a symbolic link on /usr/bin/java. The proper fix could be jenkinsci/docker-ssh-agent#74

I proposed this PR for close

[kuisathaverat]

resolved by jenkinsci/docker-ssh-agent#78