MB-10061 fix behavior of RAM Quota Settings

- maxRamMegs should show per node value, not total
- per node ram should be calculated by dividing total by the number
  of nodes with active cluster membership, not all of the nodes

Change-Id: I96a4499d6e16abb000c9424c109d8fb8e7967e18
Reviewed-on: http://review.couchbase.org/35019
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>