Add missing database close calls in tests

Change-Id: I2f304ebbef41772340a74b0682f5b6c08de73ac3
Reviewed-on: http://review.couchbase.org/27455
Reviewed-by: Aaron Miller <apage43@ninjawhale.com>
Tested-by: Aaron Miller <apage43@ninjawhale.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>