TST: buildbot-proof testing with XVFB, in case the env variable gets crunked.
TST: buildbot-proof testing with XVFB, in case the env variable gets crunked.

nilgoyyou/dipy,matthieudumont/dipy,FrancoisRheaultUS/dipy,nilgoyyou/dipy,FrancoisRheaultUS/dipy,villalonreina/dipy,StongeEtienne/dipy,StongeEtienne/dipy,villalonreina/dipy,matthieudumont/dipy