Separate out testing dependencies to be more independent of travis

* move docker-hub-helper in a general ci folder
* move installation of tools into dedicated script (will make it easier to use a different ci platform)
* mention the setup-tools script in contributing and move testing instructions in there as well

.ci/setup-tools.sh

@@ -0,0 +1,57 @@
+#!/bin/bash
+
+set -euo pipefail
+IFS=$'\n\t'
+
+HADOLINT_VERSION=1.17.1
+DOCKER_COMPOSE_VERSION=1.23.2
+TRIVY_VERSION=0.1.1
+GOSS_VERSION=0.3.7
+COMMANDER_VERSION=1.2.1
+
+if ! command -v hadolint > /dev/null; then
+	sudo curl -L "https://github.com/hadolint/hadolint/releases/download/v$HADOLINT_VERSION/hadolint-$(uname -s)-$(uname -m)" -o /usr/local/bin/hadolint
+	sudo chmod +rx /usr/local/bin/hadolint
+fi
+
+if ! command -v docker-compose > /dev/null; then
+	sudo curl -L "https://github.com/docker/compose/releases/download/${DOCKER_COMPOSE_VERSION}/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose
+	sudo chmod +rx /usr/local/bin/docker-compose
+fi
+
+if ! command -v trivy > /dev/null; then
+	wget https://github.com/knqyf263/trivy/releases/download/v${TRIVY_VERSION}/trivy_${TRIVY_VERSION}_Linux-64bit.tar.gz
+	sudo tar zxvf trivy_${TRIVY_VERSION}_Linux-64bit.tar.gz -C /usr/local/bin trivy
+fi
+
+if ! command -v goss > /dev/null; then
+	sudo curl -L https://github.com/aelsabbahy/goss/releases/download/v$GOSS_VERSION/goss-linux-amd64 -o /usr/local/bin/goss
+	sudo chmod +rx /usr/local/bin/goss
+fi
+
+if ! command -v dcgoss > /dev/null; then
+	sudo curl -L https://raw.githubusercontent.com/fbartels/goss/dcgoss-v2/extras/dcgoss/dcgoss -o /usr/local/bin/dcgoss
+	sudo chmod +rx /usr/local/bin/dcgoss
+fi
+
+if ! command -v commander > /dev/null; then
+	sudo curl -L https://github.com/SimonBaeumer/commander/releases/download/v$COMMANDER_VERSION/commander-linux-amd64 -o /usr/local/bin/commander
+	sudo chmod +rx /usr/local/bin/commander
+fi
+
+if ! command -v commander > /dev/null; then
+	sudo curl -L https://raw.githubusercontent.com/fbartels/dccommander/master/dccommander -o /usr/local/bin/dccommander
+	sudo chmod +rx /usr/local/bin/commander
+fi
+
+if ! command -v expect > /dev/null; then
+	sudo apt update && sudo apt install -y expect
+fi
+
+if ! command -v yamllint > /dev/null; then
+	sudo pip install --upgrade pip && sudo pip install yamllint
+fi
+
+if ! command -v eclint > /dev/null; then
+	npm install -g eclint
+fi