API: column family estimated histograms
API: column family estimated histograms

This patch fix an issue with the read latency estimated historam
implementation and add a call to the estimated number of sstable
histogram.

The later is not yet implemented on the datbase side.

Signed-off-by: Amnon Heiman <ed5fc74c4692051ad0b19749fd7cea6ec2d74b9e@cloudius-systems.com>

duarten/scylla,raphaelsc/scylla,kjniemi/scylla,avikivity/scylla,kjniemi/scylla,scylladb/scylla,duarten/scylla,avikivity/scylla,raphaelsc/scylla,raphaelsc/scylla,scylladb/scylla,duarten/scylla,scylladb/scylla,avikivity/scylla,kjniemi/scylla,scylladb/scylla