zdtm.py: don't umount in clean_tests_root

If we get EBUSY here, it means that we didn't umount in the test (i.e. we
didn't call fini() on some path). We should just do that instead.
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

test/zdtm.py

@@ -44,7 +44,6 @@ tests_root = None
 
 def clean_tests_root():
 	global tests_root
-	subprocess.call(["umount", tests_root])
 	if tests_root:
 		os.rmdir(tests_root)