Fix wrong test in flavor unit tests

In test_flavor_set_no_project(), we aimed to test a
situation like this: User specifies "--project" option,
but didn't specifies the project name or ID.

But in the source code, it becomes "--project ''".

The test could past because if project and property
are both None, the command will raise an exception.

Change-Id: I39567306debb901e8bad420fa2492f1b207efddc

openstackclient/tests/compute/v2/test_flavor.py

@@ -491,17 +491,15 @@ class TestFlavorSet(TestFlavor):
 
     def test_flavor_set_no_project(self):
         arglist = [
-            '--project', '',
+            '--project',
             self.flavor.id,
         ]
         verifylist = [
             ('project', ''),
             ('flavor', self.flavor.id),
         ]
-
-        parsed_args = self.check_parser(self.cmd, arglist, verifylist)
-        self.assertRaises(exceptions.CommandError, self.cmd.take_action,
-                          parsed_args)
+        self.assertRaises(tests_utils.ParserException, self.check_parser,
+                          self.cmd, arglist, verifylist)
 
     def test_flavor_set_no_flavor(self):
         arglist = [