Adjust test suite for new psutil versions

psutil 2.x and above has a lot of API changes as described in:
https://github.com/giampaolo/psutil/blob/master/HISTORY.rst

So we should work correctly with both old and new psutil
versions by using a version check and use the correct
method/attributes. This allows to eventually unlift the version
cap that starts to hurt.

Change-Id: I6b6682e3af34f43da4e397d602e9ee4e1c83970f
Related-Bug: 1645918

os_refresh_config/os_refresh_config.py

@@ -60,7 +60,12 @@ PHASES = ['pre-configure',
 
 def timeout():
     p = psutil.Process()
-    children = list(p.get_children(recursive=True))
+    try:
+        # psutils version >= 2
+        children = list(p.children(recursive=True))
+    except AttributeError:
+        children = list(p.get_children(recursive=True))
+
     for child in children:
         child.kill()