CBQE-1482 Add test to automated mem frag due to large append ops

The workload support for appending fixed size content to documents
and exponential increased size content. Also we can choose to verify
the value of each key or not to verify.
Change-Id: I6ef0ed99464ee1dff2d03d4d7d07070a2fcb8eb9
Reviewed-on: http://review.couchbase.org/27907
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Chisheng Hong <chisheng@couchbase.com>
Tested-by: Chisheng Hong <chisheng@couchbase.com>