Provide a valid list of plugins for a specific version of Jenkins

[clarsonneur]

When a Jenkins plugin requires a proper version of jenkins core, currently jplugins ignore it.

We should be able to support it.

[clarsonneur]

Yesterday, blueocean delivered blueocean version 1.11.0.
This package was forcelly requiring a new version of Java (11 instead of 1.8 currently recommended)

Jenkins is fully supported on java 1.8, and is experimental in java 1.11.

jplugins, while it do not check the required java version, download them and fails to deliver the blueocean service with error message on the java version.

It became urgent to detect the java version to ensure that those plugins won't be selected if this happens again.
On the same day, blueocean was published back to 1.11.1 requiring Java 1.8 and not java 11.

I set this issue as high.