tests: Fix test_input_accel() leaking a daemon

test_input_accel() uses umockdev-run, and killing umockdev-run doesn't
kill the child iio-sensor-proxy daemon we make it spawn, making any test
running after this one fail. As the tests are run alphabetically, we
were lucky that this test was the last one, but we can't rely on that.

Instead, use psutil to list all the children processes and kill those
before killing umockdev-run.

.gitlab-ci.yml

@@ -13,6 +13,7 @@ variables:
                 git
                 python3-gobject
                 python3-dbusmock
+                python3-psutil
                 umockdev
 
 build_stable:

tests/integration-test

@@ -23,6 +23,7 @@ import sys
 import dbus
 import tempfile
 import subprocess
+import psutil
 import unittest
 import time
 
@@ -176,6 +177,8 @@ class Tests(dbusmock.DBusTestCase):
 
         if self.daemon:
             try:
+                for child in psutil.Process(self.daemon.pid).children(recursive=True):
+                    child.kill()
                 self.daemon.kill()
             except OSError:
                 pass