Move consumer atom feed to correct API location.

When fetching info specific to a consumer our preferred API layout is to
go to /consumers/{uuid}.

This patch moves /owners/{key}/consumers/{uuid}/atom to
/consumers/{uuid}/atom.

This coincides also with /consumers/{uuid}/events which is just a
different representation of the same data.

I have verified the old API call is used in neither SAM, Satellite,
nor hosted environments.

Updated and expanded on some related spec tests.