The ColumnFamilyMetrics is used to report statistic of a column family.
This adds an adaptation for the ColumnFamilyMetrics that works with the
API that define in column_family.json
It adds the ColumnFamilyMetrics to the ColumnFamilyStore and expose the
keyspace name, so the ColumnFamilyMetrics would have access to it.
Signed-off-by: Amnon Heiman <amnon@cloudius-systems.com>