Add config parameter to have verbose logging or not.   For sync_gateway, verbose logging will turn on "HTTP", "HTTP+", "CRUD"

Change-Id: I9e0cf24d5a5898a80070e3d787b87ba0da8c1b58
Reviewed-on: http://review.couchbase.org/39313
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Li Yang <lichenyang2@gmail.com>