Description of problem:
I've just installed OCP 3.6 and I'm trying to run a very basic declarative jenkins pipleline. I'm hitting this issue [0]  due to a missing plugin "Pipeline: Model Definition". Once added the pipeline works as expected.

[0] https://issues.jenkins-ci.org/browse/JENKINS-42620


Version-Release number of selected component (if applicable):

I'm using the following jenkins image registry.access.redhat.com/openshift3/jenkins-2-rhel7@sha256:4647a54e7a4bba9f1ca3db364ae235b5e75a46e7d81f77152e0eef88de7ba440


How reproducible:


Steps to Reproduce:
1.
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Actual results:


Expected results:


Additional info:
The pipeline is as follows:

pipeline {
    agent any

    post {
      failure {
        updateGitlabCommitStatus name: 'build', state: 'failed'
      }
      success {
        acceptGitLabMR mergeCommitMessage: 'Accepted by Jenkins CI'
      }
    }

   stages{

    stage('setup') {
      steps{
        sh 'env'
        println 'Before git'
        git url: env.gitlabSourceRepoHttpUrl
      }
    }

    stage('DoWork'){
            steps{
        println "${env.gitlabSourceNamespace}/${env.gitlabSourceBranch}"
        sh 'git branch -vv'
        println "Looking to merge ${env.gitlabSourceBranch} from ${env.gitlabSourceNamespace} into ${env.gitlabTargetBranch} from ${env.gitlabTargetNamespace}"
      }
    }
   }
}