Makefile: Remove slave container from the build

Ubuntu 15.04, that the old slave cotainer is based on, is discontinued.
Remove that image from the build process, but preserve the slave
directory for now and consider to remove it later.

Change-Id: Iac6bb5e1eec2c0b55a11659052e86e7d240ee147
1 file changed
tree: 7024774ea75f7e1a625aeb230424d1c7f531ac33
  1. jenkins/
  2. jenkins-docker/
  3. worker/
  4. .gitignore