Add support for the matrix-combinations plugin

This plugin allows a user to choose which matrix combinations
they want to run, as opposed to the default behaviour where
jenkins runs all combinations

Requires the Jenkins Matrix Combinations Plugin:
https://wiki.jenkins-ci.org/display/JENKINS/Matrix+Combinations+Plugin

Change-Id: I13205c81aa11523a4c3fc373820eb74863d0c7ca
Merge "Add support for the matrix-combinations plugin"