CRM-14389 membership api - add test for fix

----------------------------------------
* CRM-14389: Get memberships api ignores membership_type_id if contact_id is present
  https://issues.civicrm.org/jira/browse/CRM-14389
Merge pull request #2848 from eileenmcnaughton/CRM-14389

CRM-14389 membership api - add test for fix + alter to 'correct fix'