UK SSO: refactor integration tests.

#### What's this PR do?
- Refactors and improves UK SSO integration tests
- Makes it easier to follow the same flow in similar tests on Canada
- Tests user profile both created from new login and signed up using registration form
![image](https://cloud.githubusercontent.com/assets/672669/4772900/d63f2cb2-5b9c-11e4-8cc4-38bf9db91585.png)

#### How should this be manually tested?
- Enable and setup DoSomething UK module
- Run `ds test uk`