Introduce new base slave with debian stretch (9)

By using a brand-new debian stretch, the image should be smaller.

Stretch was only released in around June 2017 and is supported
for at least 5 years.

This pins the chrome version to 63.0.3239.108 so we will need to
mannualy upgrade it when new releases are done.

Bug: Issue 8023
Change-Id: Ia7f8f36ed7207e37cbcf779fe37fa823c952c8cc
7 files changed
tree: 9810cac89a3e66877c3d12605d4b1e6ee2b967fd
  1. jenkins/
  2. jenkins-docker/
  3. .gitignore