Use the email from the session instead of sending it as a parameter.

* Corrects the test accordingly.
* The getPatients API still gets an email since it used for both all
  patients and a specific one by email.
* Adds the logout function in the spec helper. The logout is needed since
  it invalidates the session and the email is taken from the session.
  Each test creates a new user and this shouldn't be done while you're
  already signed in as another user.