CCBC-507: Add vbucket test cases for malformed/empty configs

Change-Id: I0d261f71887337cddfdd8a3419911150d5c49c88
Reviewed-on: http://review.couchbase.org/42447
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>