Add github actions to test against a matrix of bazel versions

Brought up in the discussion of bazelbuild#463, was that testing against multiple
bazel versions with bazelci didn't seem possible without a fair bit of
work.

Judging based on usage that I have seen, we probably moved too quickly
on bumping the minimum version to 3.0.0, but until we can actually test
against our minimum version, we won't be able to reasonably version
breaking changes as suggested by bazelbuild#415.

This initial PR leaves a lot of on the table in terms of potential
optimizations, and is fixed on Ubuntu 20.04 LTS for the moment.

Author: David Freese

.github/actions/bazel/Dockerfile

@@ -0,0 +1,18 @@
+FROM ubuntu:focal-20200423
+
+COPY bazel.sh /bazel.sh
+
+RUN apt-get update \
+  && apt-get install -y \
+    curl \
+    gnupg2 \
+    wget
+
+RUN curl https://bazel.build/bazel-release.pub.gpg | apt-key add - \
+  && echo "deb [arch=amd64] https://storage.googleapis.com/bazel-apt stable jdk1.8" > /etc/apt/sources.list.d/bazel.list \
+  && curl https://packages.cloud.google.com/apt/doc/apt-key.gpg | apt-key --keyring /usr/share/keyrings/cloud.google.gpg add - \
+  && echo "deb [signed-by=/usr/share/keyrings/cloud.google.gpg] https://packages.cloud.google.com/apt cloud-sdk main" > /etc/apt/sources.list.d/google-cloud-sdk.list
+
+RUN apt-get update
+
+ENTRYPOINT ["/bazel.sh"]

.github/actions/bazel/action.yml

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+name: "Bazel"
+description: "Run a bazel command on a particular directory"
+author: "David Freese"
+inputs:
+  version:
+    description: "The version of bazel to use"
+    required: true
+  command:
+    description: "The bazel command to run"
+    required: true
+  arguments:
+    description: "Arguments to pass to bazel after the bazel command"
+    required: false
+  directory:
+    description: "The directory in which to run the command"
+    required: false
+  targets:
+    description: "Targets on which to run the command"
+    required: false
+  query:
+    description: "A Bazel query describing which"
+    required: false
+runs:
+  using: "docker"
+  image: "Dockerfile"

.github/actions/bazel/bazel.sh

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+#!/bin/bash -eux
+
+if [[ -n "${INPUT_ARGUMENTS:-""}" ]]; then
+  INPUT_COMMAND+=(" ${INPUT_ARGUMENTS}")
+fi
+
+apt-get install -y "bazel-${INPUT_VERSION}"
+
+if [[ -n "${INPUT_DIRECTORY:-""}" ]]; then
+  cd "${INPUT_DIRECTORY}"
+fi
+
+if [[ -n "${INPUT_TARGETS:-""}" ]]; then
+  INPUT_TARGETS="//..."
+fi
+if [[ -n "${INPUT_QUERY:-""}" ]]; then
+  INPUT_TARGETS=$("bazel-${INPUT_VERSION}" query -- "${INPUT_QUERY}")
+fi
+
+# leave targets unquoted to allow multi-line query output to be a single-line
+# input here.
+"bazel-${INPUT_VERSION}" "${INPUT_COMMAND}" -- ${INPUT_TARGETS}

.github/workflows/ci.yaml

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+name: CI
+on:
+  push:
+
+jobs:
+  bazel:
+    name: Build/Test
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        # The two most recent versions and the current min supported version
+        version: ["3.0.0", "3.6.0", "3.7.0"]
+        command: ["build", "test"]
+    steps:
+      - name: Checkout
+        uses: verily-src/checkout@v2
+      - name: Run Bazel
+        uses: "./.github/actions/bazel"
+        with:
+          version: ${{ matrix.version }}
+          command: ${{ matrix.command }}
+          query: "//... - @examples//... - attr('tags', 'manual', //...)"