sanity-check: print a process tree in terms of both ppid and cgroup

This should help to debug situations where a process has been
started the wrong way, for example in T1984.

Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D3648

common/sanity-check

@@ -24,6 +24,11 @@ fail () {
     echo "TEST_RESULT:fail:$tag:$*" >&2
 }
 
+# This is just for information, so we ignore the exit status. Minimal
+# images might legitimately not have these tools.
+systemd-cgls -al --no-pager || :
+pstree -lpu || :
+
 getent passwd root || fail getent-passwd-root
 getent passwd user || fail getent-passwd-user