Prior to this commit, the vagrant snapshot plugin would save snapshots
with existing names which lead to duplicate snapshot names being saved.
This commit fixes that by checking to see if the given snapshot name
already exists and if so, fails telling the user the given snapshot name
already exists. If a user passes a --force flag, vagrant will first
delete the existing snapshot, and take a new one with the given name.
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)
Brian Cain
Jon Topper
Mitchell Hashimoto