Rename _vagrant to vagrant

Apparently the idea to prefix a package with an underscore is not that
smart as I thought. Yes `go test` does not run it by default when you
run `go test ./...` but also other commands like `go mod tidy` do not
work consistently.

Nothing changes in practice. By default only unit tests run. Setting the
new environment variable: `TEST_WITH_VAGRANT` you include the test who
uses vagrant.

Signed-off-by: Gianluca Arbezzano <gianarb92@gmail.com>

.github/workflows/vagrant-packet.yaml

@@ -8,10 +8,15 @@ jobs:
   vagrant-setup:
     if: contains(github.event.pull_request.labels.*.name, 'ci-check/vagrant-setup')
     runs-on: vagrant
+    env:
+      TEST_WITH_VAGRANT: "yes"
     steps:
       - name: Checkout
         uses: actions/checkout@v2
+      - name: Cleanup state directory
+        run: |
+          rm -rf ./deploy/state
       - name: Vagrant Test
         run: |
           export VAGRANT_DEFAULT_PROVIDER="virtualbox"
-          go test --timeout 1h -v ./test/_vagrant
+          go test --timeout 1h -v ./test/vagrant