MB-100: improve linux-specific info gathering

I've made a pass over stats and other info we gather in cbcollect_info
and added some things that I remember missing from some
CBSEs. Hopefully it'll improve our CBSE investigations.

Change-Id: Iff92bf23c08afec657ea525ee82de0a0bf70c0f0
Reviewed-on: http://review.couchbase.org/25163
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>