Add docker image for vagrant-libvirt (#1149)

Provide a docker image that supports execution of vagrant-libvirt
provided the host system has docker and libvirt installed. This can help
side step many of the library compatibility issues experienced by users
by providing an alternative way to run the latest code should their
distribution not have a natively packaged vagrant.

.github/workflows/build.yml

@@ -0,0 +1,82 @@
+name: ci
+
+on:
+  push:
+    branches:
+      - '**'
+    tags:
+      - 'v*'
+  pull_request:
+
+jobs:
+  main:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v2
+      -
+        name: Prepare
+        id: prep
+        run: |
+          DOCKER_IMAGE=vagrantlibvirt/vagrant-libvirt
+          VERSION=noop
+          if [ "${{ github.event_name }}" = "schedule" ]; then
+            VERSION=nightly
+          elif [[ $GITHUB_REF == refs/tags/* ]]; then
+            VERSION=${GITHUB_REF#refs/tags/}
+          elif [[ $GITHUB_REF == refs/heads/* ]]; then
+            VERSION=$(echo ${GITHUB_REF#refs/heads/} | sed -r 's#/+#-#g')
+            if [ "${{ github.event.repository.default_branch }}" = "$VERSION" ]; then
+              VERSION=edge
+            fi
+          elif [[ $GITHUB_REF == refs/pull/* ]]; then
+            VERSION=pr-${{ github.event.number }}
+          fi
+          TAGS="${DOCKER_IMAGE}:${VERSION}"
+          if [[ $VERSION =~ ^v[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$ ]]; then
+            MINOR=${VERSION%.*}
+            MAJOR=${MINOR%.*}
+            TAGS="$TAGS,${DOCKER_IMAGE}:${MINOR},${DOCKER_IMAGE}:${MAJOR},${DOCKER_IMAGE}:latest"
+          elif [ "${{ github.event_name }}" = "push" ]; then
+            TAGS="$TAGS,${DOCKER_IMAGE}:sha-${GITHUB_SHA::8}"
+          fi
+          echo ::set-output name=version::${VERSION}
+          echo ::set-output name=tags::${TAGS}
+          echo ::set-output name=created::$(date -u +'%Y-%m-%dT%H:%M:%SZ')
+      -
+        name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+      -
+        name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+        with:
+          driver-opts: image=moby/buildkit:master
+
+      -
+        name: Login to DockerHub
+        if: github.event_name != 'pull_request'
+        uses: docker/login-action@v1 
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      -
+        name: Build and push
+        id: docker_build
+        uses: docker/build-push-action@v2
+        with:
+          platforms: linux/amd64
+          push: ${{ github.event_name != 'pull_request' }}
+          tags: ${{ steps.prep.outputs.tags }}
+          labels: |
+            org.opencontainers.image.title=${{ github.event.repository.name }}
+            org.opencontainers.image.description=${{ github.event.repository.description }}
+            org.opencontainers.image.url=${{ github.event.repository.html_url }}
+            org.opencontainers.image.source=${{ github.event.repository.clone_url }}
+            org.opencontainers.image.version=${{ steps.prep.outputs.version }}
+            org.opencontainers.image.created=${{ steps.prep.outputs.created }}
+            org.opencontainers.image.revision=${{ github.sha }}
+            org.opencontainers.image.licenses=${{ github.event.repository.license.spdx_id }}
+      -
+        name: Image digest
+        run: echo ${{ steps.docker_build.outputs.digest }}