Use our own builder to speed-up a bit, remove stretch build

2 jobs for master in 5 minutes and 21 seconds (queued for 7 minutes and 26 seconds)
Name Stage Failure
failed
build-jessie Test
dpkg-source: warning: ignoring deletion of file octonet.egg-info/dependency_links.txt, use --include-removal to override
dpkg-source: info: local changes detected, the modified files are:
octonet/.gitlab-ci.yml
dpkg-source: error: aborting due to unexpected upstream changes, see /tmp/octonet_10.0.4-1.diff.Ikkhgk
dpkg-source: info: you can integrate the local changes with dpkg-source --commit
dpkg-buildpackage: error: dpkg-source -b octonet gave error exit status 2
debian/rules:21: recipe for target 'debsrc' failed
make: *** [debsrc] Error 2
ERROR: Job failed: exit code 1