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