PYCBC-171 Ask server to close connection

Change-Id: Ib32ab9d9935115f39fa22bc3fcdc60335b5cd090
Reviewed-on: http://review.couchbase.org/28085
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>