Currently, "response completed with error" log lines include an
`auth.user.name` key, but successful "response completed" lines do not
include this, because they are logged a few stack frames up where
`auth.user.name` is not present on the `Context`. Move the successful
request logging inside the `dispatcher` closure, where the logger on the
context automatically includes this key.
Signed-off-by: Aaron Lehmann <alehmann@netflix.com>