Run integration tests in Travis

Travis now offers /dev/kvm, and its machines are powerful enough to run
our browser integration tests, at least for small projects.

Building an RPM on the Ubuntu host environment is a bit tricky, as there
are no installed RPMs. Thus ignore the BuildRequires, and install
appstream-util explicitly. In the future, the rpm/deb build should
happen inside the VM (like Cockpit does).

Add two scenarios for current Fedora and CentOS 8.

Switch to the "minimal" environment to make the test easier to reproduce
locally and more explicit.

Closes #386

.travis.yml

@@ -1,12 +1,31 @@
 dist: focal
-sudo: false
-language: node_js
-node_js:
-  - "lts/*"
+sudo: true
+language: minimal
 addons:
   apt:
     packages:
+      - appstream-util
+      - chromium-browser
+      - curl
+      - git
+      - libvirt-daemon-system
+      - npm
+      - python3-libvirt
+      - qemu-kvm
+      - qemu-utils
+      - rpm
       - sassc
+env:
+  - TEST_OS=fedora-33
+  - TEST_OS=centos-8-stream
 script:
-  - make
+  # HACK: /dev/kvm is root:kvm 0660 by default
+  - sudo chmod 666 /dev/kvm
+
+  # test PO template generation
   - make po/starter-kit.pot
+
+  # FIXME: build rpm inside VM; no installed rpms on Travis Ubuntu environment
+  - sed -i '/^BuildRequires:/d' *.spec.in
+
+  - TEST_JOBS=$(nproc) make check

README.md

@@ -80,6 +80,13 @@ You can also run the test against a different Cockpit image, for example:
 
     TEST_OS=fedora-32 make check
 
+These tests can be run in [Travis CI](https://travis-ci.com/). The included
+[travis.yml](./.travis.yml) runs the integration tests for two operating
+systems (Fedora and CentOS 8). Note that if/once your project grows bigger, or
+gets frequent changes, you likely need to move to a paid account, or different
+infrastructure with more capacity. Talk to the
+[Cockpit developers](https://cockpit-project.org/) if you are interested in that.
+
 # Customizing
 
 After cloning the Starter Kit you should rename the files, package names, and