Add CORS and HTTP status code test for ListReferenceBases

[jeromekelleher]

CORS support is required for servers to support JavaScript clients. Tests verifying the server's CORS support are in tests/unit/test_views.py, which tests other high-level HTTP related things (this test module is now poorly named, and should really be test_http.py or something; the hackathon isn't the time for this sort of refactor though).

• Edit the tests/unit/test_views.py, and find the testCors function. Run the test using nosetests -vs tests/unit/test_views.py:TestFrontend.testCors.
• Add a check to run the ListReferenceBases request. Remove the TODO.
• Add a function testListReferenceBases that follows the pattern of testGetVariantSet to ensure we get the right HTTP responses. The ListRefernenceBases method is defined in the schemas, and is an oddball as it doesn't follow the conventions of other server endpoints.
• Optional The requirement for CORS support is not documented anywhere in the protocol. Open a documentation issue on the schemas repo, requesting clarification on this point.

[dcolligan]

Looks like the list reference bases endpoint is already tested (self.sendReferenceBasesList) but these four endpoints are not:

1) reference sets search 2) read group sets search 3) call sets search 4) call sets get