Remove customized require behaviors and modify the bin executable
to check for missing tools that Vagrant expects to exist when
running outside of an installer.
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)
