Create Jenkinsfile for use with tez-multibranch (github yetus integration)

Clone hadoop-multibranch to tez-multibranch https://ci-hadoop.apache.org/job/tez-multibranch/

Couple of choices to base Jenkinsfile from.

Scan will need a Jenkins file to correctly start builds based on github PR.
Hadoop Jenkinsfile
https://github.com/apache/hadoop/blob/trunk/dev-support/Jenkinsfile

HBase Jenkinsfile
https://github.com/apache/hbase/blob/master/dev-support/Jenkinsfile_GitHub