In our test environments, it's good to be able to roll back to the same,
anonymous, snapshot repeatedly. This patch adds a `--no-delete` option
to the `snapshot pop` command allowing this.
This makes the new core snapshot behaviour more consistent with what we
were doing with vagrant-multiprovider-snap
(https://github.com/scalefactory/vagrant-multiprovider-snap)
Jon Topper
Mitchell Hashimoto