Test for COUCHDB-1697. Showing how the etag breaks cors
(cherry picked from commit 02357223d3618467494a858ec9bae38352238261)
Check that the content-type from the RequestHeaders is not undefined. Fixes COUCHDB-1697
(cherry picked from commit bc3ef5b8cfd58b9d07868c1267c4099f994e53d8)