Bug 1032752 - [testing] Test that an Existing User can Update Profile

Test case to verify users can edit their profile details.
In fact, what would be best for both of these is to capture the existing values (`existing_user['profile']['name']` and `existing_user['profile']['username']`) and then append something (timestamp related) to them. That way you can guarantee that the new values are different from the existing values. Otherwise the test is relying on information from outside the test (i.e., what the initial username and name were set to during setup).