TST: update Travis config to use container infrastructure.
TST: update Travis config to use container infrastructure.

See Travis docs for details:
http://docs.travis-ci.com/user/migrating-from-legacy/?utm_source=legacy-notice&utm_medium=banner&utm_campaign=legacy-upgrade

demianw/dipy,sinkpoint/dipy,StongeEtienne/dipy,StongeEtienne/dipy,sinkpoint/dipy,FrancoisRheaultUS/dipy,nilgoyyou/dipy,nilgoyyou/dipy,JohnGriffiths/dipy,FrancoisRheaultUS/dipy,villalonreina/dipy,jyeatman/dipy,matthieudumont/dipy,JohnGriffiths/dipy,demianw/dipy,villalonreina/dipy,matthieudumont/dipy,jyeatman/dipy