ci(cirrus): use cirrus-ci alongisde travis-ci

* Based on response from Cirrus CI:
  - fkorotkov/nginx-formula#1

.cirrus.yml

@@ -0,0 +1,25 @@
+docker_builder:
+  name: Test $INSTANCE
+  env:
+    matrix:
+      - INSTANCE: default-debian-9-2019-2-py3
+      - INSTANCE: default-ubuntu-1804-2019-2-py3
+      - INSTANCE: default-centos-7-2019-2-py3
+      - INSTANCE: default-fedora-29-2019-2-py3
+      - INSTANCE: default-opensuse-leap-15-2019-2-py3
+      - INSTANCE: default-debian-9-2018-3-py2
+      - INSTANCE: default-ubuntu-1604-2018-3-py2
+      - INSTANCE: default-centos-7-2018-3-py2
+      - INSTANCE: default-fedora-29-2018-3-py2
+      # TODO: Use this when fixed instead of `opensuse-leap-42`
+      # Ref: https://github.com/netmanagers/salt-image-builder/issues/2
+      # - INSTANCE: default-opensuse-leap-15-2018-3-py2
+      - INSTANCE: default-opensuse-leap-42-2018-3-py2
+      - INSTANCE: default-debian-8-2017-7-py2
+      - INSTANCE: default-ubuntu-1604-2017-7-py2
+      # TODO: Enable after improving the formula to work with other than `systemd`
+      - INSTANCE: default-centos-6-2017-7-py2
+      - INSTANCE: default-fedora-28-2017-7-py2
+      - INSTANCE: default-opensuse-leap-42-2017-7-py2
+  bundle_install_script: bundle install
+  verify_script: bundle exec kitchen verify $INSTANCE

.travis.yml

@@ -1,42 +1,8 @@
 stages:
-  - test
   - commitlint
   - name: release
     if: branch = master AND type != pull_request
 
-sudo: required
-cache: bundler
-language: ruby
-
-services:
-  - docker
-
-# Make sure the instances listed below match up with
-# the `platforms` defined in `kitchen.yml`
-env:
-  matrix:
-    - INSTANCE: default-debian-9-2019-2-py3
-    - INSTANCE: default-ubuntu-1804-2019-2-py3
-    - INSTANCE: default-centos-7-2019-2-py3
-    - INSTANCE: default-fedora-29-2019-2-py3
-    - INSTANCE: default-opensuse-leap-15-2019-2-py3
-    - INSTANCE: default-debian-9-2018-3-py2
-    - INSTANCE: default-ubuntu-1604-2018-3-py2
-    - INSTANCE: default-centos-7-2018-3-py2
-    - INSTANCE: default-fedora-29-2018-3-py2
-    # TODO: Use this when fixed instead of `opensuse-leap-42`
-    # Ref: https://github.com/netmanagers/salt-image-builder/issues/2
-    # - INSTANCE: default-opensuse-leap-15-2018-3-py2
-    - INSTANCE: default-opensuse-leap-42-2018-3-py2
-    - INSTANCE: default-debian-8-2017-7-py2
-    - INSTANCE: default-ubuntu-1604-2017-7-py2
-    - INSTANCE: default-centos-6-2017-7-py2
-    - INSTANCE: default-fedora-28-2017-7-py2
-    - INSTANCE: default-opensuse-leap-42-2017-7-py2
-
-script:
-  - bundle exec kitchen verify ${INSTANCE}
-
 jobs:
   include:
     # Define the commitlint stage