Similar to https://issues.jenkins-ci.org/browse/JENKINS-50168 and https://issues.jenkins-ci.org/browse/JENKINS-27327  BUT both of those tickets got distracted with the parameterized branch name, while the polling branch issue I think is distinct.

Problem:

When using pollscm in a pipeline job, the plugin will always poll with the branch that was configured on the last job run.  

Reproduction steps:

• Create an empty git repo
• Create a pipeline job file in the git repo on the master branch
• Create a branch off of master in the git repo
• Create a pipeline job in jenkins
• Configure your pipeline job to poll (every minute is usually good to test with)
• Configure your pipeline job to use the pipeline file you have checked in to master
• Run your job
• On your jenkins master vm navigate to the job folder E.G. /var/lib/jenkins/jobs/<jobname>  (if you are using the default ubuntu package for instance)
• Validate that scm-polling.log is looking at your master branch
• Update your pipeline job in Jenkins to point to your second branch
• On your jenkins vm, validate that the timestamp on scm-polling.log has updated
• Validate that the plugin is still polling against master