[JENKINS-21268] [JENKINS-14727] Make maven-plugin a mandatory dependency.
[JENKINS-21268] [JENKINS-14727] Make maven-plugin a mandatory dependency.

Workaround for JENKINS-21268. The maven plug-in can't be optional without breaking the API. This issue needs to be adressed in  2.x release.

SvenLuebke/warnings-plugin,SvenLuebke/warnings-plugin,jenkinsci/warnings-plugin,SvenLuebke/warnings-plugin,jenkinsci/warnings-plugin,jenkinsci/warnings-plugin