Turn-off Xvfb auto-display to avoid flaky failures

At times Xvfb is failing because of the inability to start
within 10 seconds.
Set the timeout to 30 seconds and avoid the auto-discover displays
to minimise the probability of future flaky failures.

Change-Id: I1913b4dc437107194b52c39f5b4b7f2704c0577d
2 files changed
tree: 2cb578d94dfefff1be2c069a05cb0733185f32a9
  1. jenkins/
  2. jenkins-docker/
  3. .gitignore