tools/scyllatop: Sort metrics by name
tools/scyllatop: Sort metrics by name

This makes the output much easier to read, especially if you have tons
of metrics specified.

Message-Id: <e82283d96eae584b8f857a3f4df55f3de4e44db4@scylladb.com>

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