* The vagrant-spec gem is installed as part of bundle install so
there's no need to install it separately. Remove those extra steps
and invoke it with bundle exec instead.
* The binstub for vagrant does not work with `--standalone` in CI, but
the one generated w/o `--standalone` works fine. This also seems to
work in dev, so we'll just switch to that one.
* Fetch all tags in CI to make sure we're getting proper version
numbers in our build (based off `git describe`).
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