Add test for lcb_dump()

Change-Id: I5a1a02c7f76557ede7b22dcfa4016cfe1b875838
Reviewed-on: http://review.couchbase.org/42546
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>