zdtm.py: run --clean hook on test failure

It seems to me most of the clean hooks (used by cgroup*, macvlan* cr_veth*
and mnt_tracefs* were all designed to be run to clean up after the test, no
matter whether it failed or succeeded. Let's always run them, so Andrei
doesn't hate me :D

travis-ci: success for zdtm.py: run --clean hook on test failure
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
CC: Andrei Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

test/zdtm.py

@@ -1265,6 +1265,7 @@ def do_run_test(tname, tdesc, flavs, opts):
 			print_sep("Test %s FAIL at %s" % (tname, e.step), '#')
 			t.print_output()
 			t.kill()
+			try_run_hook(t, ["--clean"])
 			if cr_api.logs():
 				add_to_report(cr_api.logs(), tname.replace('/', '_') + "_" + f + "/images")
 			if opts['keep_img'] == 'never':