MB-100: added file fragmentation info to cbcollect_info output

Change-Id: I4a17ec4c1fa26c8686be164acda2408ad99a4a73
Reviewed-on: http://review.couchbase.org/25709
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>