Update marketplace_api.py to expect status code 201 when adding content ratings

To support the change introduced in https://github.com/mozilla/zamboni/pull/1801
Merge pull request #448 from bobsilverberg/api_fix_2

Update marketplace_api.py to expect status code 201 when adding content ratings
Added test for anonymously reporting abuse.
Removed nondestructive mark from test.
Merge pull request #449 from mediocrity/report_abuse_test

Added test for anonymously reporting abuse.