Collapse integration test workflows into one config (#1855)

* Collapse integration test workflows into one config

Remove last traces of Travis, including env vars and `make travis-setup`
and badges in README

* fix lint

* make integration tests pass on PRs

scripts/travis-setup.sh

@@ -1,25 +0,0 @@
-#!/bin/bash
-# Copyright 2020 Google LLC
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-set -ex
-
-curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
-sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
-sudo apt-get update
-sudo apt-get -y -o Dpkg::Options::="--force-confnew" install docker-ce
-curl -LO https://storage.googleapis.com/container-diff/latest/container-diff-linux-amd64 && chmod +x container-diff-linux-amd64 && sudo mv container-diff-linux-amd64 /usr/local/bin/container-diff
-
-mkdir -p $HOME/.docker/
-echo '{}' > $HOME/.docker/config.json