use 2 blank lines before class declaration

according to PEP 8.

Change-Id: I05c99dfc10232ad667ba6c12d21653abb6731b78
Reviewed-on: http://review.couchbase.org/34104
Reviewed-by: Aaron Miller <apage43@ninjawhale.com>
Tested-by: Aaron Miller <apage43@ninjawhale.com>