Set errstr when failing to parse json.
Set errstr when failing to parse json.

Change-Id: I79cad554cc5ae3261f9e3e0091a5624da9d45533
Reviewed-on: http://review.northscale.com:8080/637
Reviewed-by: Steve Yen <ef850f73f7832052d3c6d9b5ddd3a1716d9a57f1@gmail.com>
Tested-by: Steve Yen <ef850f73f7832052d3c6d9b5ddd3a1716d9a57f1@gmail.com>

couchbase/libvbucket,zbase/libvbucket,zbase/libvbucket,membase/libvbucket,zbase/libvbucket