Record telenium/kivy video

- add a ffmpeg process to kivy tests if it detects running inside docker
- this approach can be reused for other tests that may benefit from a
  video
- it may be possible to do this in bash, outside of python, but that
  would exacerbate the process synchronisation issues, as outlined here:
  - X server must be running before ffmpeg starts, otherwise ffmpeg
    can't record and quits
  - ffmpeg must end before the X server ends, as otherwise it segfaults
    and video will be incomplete
  - ffmpeg must start before the actual tests start and stop after the
    tests stop, otherwise a part of the tests will be missing from the
    recording
- this approach I chose here avoids most synchronisation issues.
  If ffmpeg takes more than 2 seconds to start recording (unlikely), a
  part of the video will be missing. Also if for some reason ffmpeg is
  too slow, then also we may end up with a truncated video, at the end.
- I chose lossless vp9 codec with webm format, this appears to work on
  firefox and chrome. Safari refuses to show the video even though it
  should be supported.

.buildbot/kivy/Dockerfile

@@ -11,7 +11,7 @@ RUN apt-get install -yq \
     build-essential libcap-dev libssl-dev \
     libmtdev-dev libpq-dev \
     python3-dev python3-pip python3-virtualenv \
-    xvfb
+    xvfb ffmpeg
 
 RUN ln -sf /usr/bin/python3 /usr/bin/python
 

tests-kivy.py

@@ -4,6 +4,10 @@ import random  # noseq
 import sys
 import unittest
 
+from os import environ, mkdir
+from subprocess import Popen, TimeoutExpired
+from time import sleep
+
 
 def unittest_discover():
     """Explicit test suite creation"""
@@ -13,5 +17,27 @@ def unittest_discover():
 
 
 if __name__ == "__main__":
+    with open("/proc/self/cgroup", "rt", encoding='ascii', errors='replace') as f:
+        in_docker = "docker" in f.read()
+
+    if in_docker:
+        try:
+            mkdir("../out")
+        except FileExistsError:  # flake8: noqa:F821
+            pass
+
+        ffmpeg = Popen([  # pylint: disable=consider-using-with
+                       "ffmpeg", "-y", "-nostdin", "-f", "x11grab", "-video_size", "vga",
+                       "-draw_mouse", "0", "-i", environ['DISPLAY'],
+                       "-codec:v", "libvpx-vp9", "-lossless", "1", "-r", "30",
+                       "../out/test.webm"
+                       ])
+        sleep(2)  # let ffmpeg start
     result = unittest.TextTestRunner(verbosity=2).run(unittest_discover())
+    if in_docker:
+        ffmpeg.terminate()
+        try:
+            ffmpeg.wait(10)
+        except TimeoutExpired:
+            ffmpeg.kill()
     sys.exit(not result.wasSuccessful())