Add Molecule CI test for nvidia driver role

Right now this is just a basic "does the install succeed?" test, with no
special verification going on.

- Add auto-generated molecule test
- Configure Molecule to test all of
  - CUDA repo on CentOS 7 and 8
  - CUDA repo on Ubuntu 18.04 and 20.04
  - Canonical repo on Ubuntu 18.04 and 20.04
- Add Github Action to test in CI

.github/workflows/molecule.yml

@@ -0,0 +1,15 @@
+---
+on:
+  - push
+  - pull_request
+
+jobs:
+  build:
+    runs-on: ubuntu-20.04
+    steps:
+      - name: checkout
+        uses: actions/checkout@v2
+        with:
+          path: "${{ github.repository }}"
+      - name: molecule
+        uses: robertdebock/molecule-action@2.7.2