Move all uses of BUILD_NUMBER to BUILD_ID

[stronk7]

Since long ago, the "official" name of the build number env variable in Jenkins is BUILD_ID.

While the previous BUILD_NUMBER one still works perfectly, right now we have a mix of uses. This is about to move all to be BUILD_ID (that is the official one and the one used by our newer tools).

Ref.: https://www.jenkins.io/doc/book/pipeline/jenkinsfile/#using-environment-variables

Ciao :-)