add box的时候默认保存在 C:\Users\xxx\.vagrant.d
VAGRANT_HOME can be set to change the directory where Vagrant stores global state. By default, this is set to ~/.vagrant.d. The Vagrant home directory is where things such as boxes are stored, so it can actually become quite large on disk.
通过设置VAGRANT_HOME环境变量改变默认位置
setx VAGRANT_HOME "X:/your/path"
setx VAGRANT_HOME "X:/your/path" /M （系统变量）