better log janitor source data for bucket config update decisions

In MB-11890 it looks like we're dealing with the case when vbucket is
seen in vbuckets stats after it is deleted. But I have to infer it
from the code and from other log messages. Having all incoming state
explicitly is going to be helpful for cases like that.

Change-Id: I7195c3b0f0fc319377762c95440881150fcd4ee1
Reviewed-on: http://review.couchbase.org/40603
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>