openqa/worker: install ffmpeg-free

I'm adding this as a Recommends: for os-autoinst, but want to
get it on the workers now. Having it installed gives us better
videos of test runs (the internal video encoder is a bit wonky
and produces videos that have errors which make jumping around
within the video not work properly).

Signed-off-by: Adam Williamson <awilliam@redhat.com>

roles/openqa/worker/tasks/main.yml

@@ -69,7 +69,7 @@
 
 - name: Install required packages
   package:
-    name: ['openqa-worker', 'os-autoinst']
+    name: ['openqa-worker', 'os-autoinst', 'ffmpeg-free']
     state: latest
     enablerepo: "{{ openqa_repo }}"
   notify: