travis: add an osbuild test

Actually test the tools. This simply runs a noop stage followed by
a noop assembler.

Signed-off-by: Tom Gundersen <teg@jklm.no>

.travis.yml

@@ -2,9 +2,13 @@ dist: bionic
 language: python
 python:
   - "3.7"
+before_install:
+  - sudo apt-get install -y systemd-container
 install:
   - pip install pylint
 jobs:
   include:
     - name: pylint
       script: pylint osbuild osbuild-run assemblers/* stages/*
+    - name: pipeline-noop
+      script: sudo env "PATH=$PATH" python3 -m osbuild --libdir . --output . samples/noop.json