MB-9514: start stale histo epoch cleaner at right time

It's very clearly a bad idea to do it before ets table is created. And
fix is obvious.

Change-Id: I0d517c53e88a0d9de2081043e813d3e80cb61420
Reviewed-on: http://review.couchbase.org/30265
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>