CBD-1412: report fragmentation ratio after revAB test

Change-Id: Ia29284271a6f4caa80b69163351c54472fc5edf8
Reviewed-on: http://review.couchbase.org/40102
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Dave Rigby <daver@couchbase.com>
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>