add a test for wsapi/email_addition_status (which was not being called previously)

I was looking at code coverage for browserid, and we were not ever calling /wsapi/email_addition_status (except for utter failure in stalled-mysql-test). 

1. I suppose I could have retrofitted some existing tests to add this call, but I don't mind having a distinct test for this wsapi.

2. There is another code path in email_addition_status not covered by this test, but reaching it would require changes to the lib/db code to expose a call, which I've done, but I'll put that in a separate pull requests after this one lands (or is rejected ;-) ).

@shane-tomlinson please note if I'm not using this wsapi the right way. Thanks.