API: storage_service get_logging_level
API: storage_service get_logging_level

This patch adds the get_loggin_level command that returns a map between
the log name and its level.
To test the API do:
curl -X GET "http://localhost:10000/storage_service/logging_level"

this would enable the `nodetool getlogginglevels` command.

Signed-off-by: Amnon Heiman <ed5fc74c4692051ad0b19749fd7cea6ec2d74b9e@scylladb.com>
Message-Id: <1453365106-27294-3-git-send-email-ed5fc74c4692051ad0b19749fd7cea6ec2d74b9e@scylladb.com>

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