Use http_urlmode=2 for tests with mock

This works around a bug in the mock where a 404 would erroneously close
the connection.

Change-Id: Id68cf2ddc39c05b0b91943008f45d630d021bf4a
Reviewed-on: http://review.couchbase.org/42061
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Dave Rigby <daver@couchbase.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>