Jenkins now requires Java 8 after version 2.54, according to blog posts. However, the Debian package still has a dependency on Java 7, as such Apt upgraded it, leaving it in a horribly broken state because the folks behind Jenkins forgot to package their application correctly.

I've forbidden the package via apt and suspended puppet, but this needs to be fixed properly, probably via puppet. I'm guessing a new release is going to come out soon, with an updated dependency on Java 8, which will hopefully fail to install in the normal way, but this isn't guaranteed

Something like this is probably needed:

package { jenkins :
  ensure => '2.53'; # 2.54 requires Java 8, which we don't have on trusty.
}

Also related: https://issues.jenkins-ci.org/browse/JENKINS-43495