add download bionic image

ci-scripts/createVM.sh

@@ -9,6 +9,7 @@ echo $result
 if [ "$result" != "" ];then
     uvt-kvm destroy $VM_NAME  ## if exist testing vm, then remove it
 fi
+uvt-simplestreams-libvirt sync arch=amd64 release=bionic --source=https://mirrors.tuna.tsinghua.edu.cn/ubuntu-cloud-images/daily
 ##创建一个虚拟机用于承载测试；
 uvt-kvm create vmtest release=bionic --memory 8192 --disk 80 --cpu 4 --ssh-public-key-file ~/.ssh/id_rsa.pub
 uvt-kvm wait $VM_NAME