Python 3.10: Subcomand help test fix

In Python 3.10, "Optional arguments" becomes "Options". This
patch fixes that. FYI, this was reported against my Debian package:

https://bugs.debian.org/1002431

and currently, the package build against Python 3.9 and 3.10, so
I'm sure this patch works in both cases.

Change-Id: I76dc4077dde648d1a5589b49bf697470063ca2c1

zunclient/tests/unit/test_shell.py

@@ -101,10 +101,14 @@ class ShellTest(utils.TestCase):
                             matchers.MatchesRegex(r, re.DOTALL | re.MULTILINE))
 
     def test_help_on_subcommand(self):
+        if sys.version_info >= (3, 10):
+            options_name = 'Options'
+        else:
+            options_name = 'Optional arguments'
         required = [
             r'.*?^usage: zun create',
             r'.*?^Create a container.',
-            r'.*?^Optional arguments:',
+            r'.*?^' + options_name + ':',
         ]
         stdout, stderr = self.shell('help create')
         for r in required: