Update travis.yml with the vre integration test
Update travis.yml with the vre integration test

ioannisstenos/e-science,VFoteinos/e-science,KPetsas/e-science,ibyron/e-science,ibyron/e-science,ioannisstenos/e-science,VFoteinos/e-science,KPetsas/e-science,VFoteinos/e-science,ibyron/e-science,ibyron/e-science,KPetsas/e-science,grnet/e-science,grnet/e-science,KPetsas/e-science,VFoteinos/e-science,ioannisstenos/e-science,ioannisstenos/e-science,KPetsas/e-science,grnet/e-science,ioannisstenos/e-science,ibyron/e-science,grnet/e-science,grnet/e-science,VFoteinos/e-science