io_tester: Name sched classes by workload name
io_tester: Name sched classes by workload name

This makes metrics get the workload name as well, which, in turn,
will make it possible for the io-tester to find this metrics and
report as a part of the workload results.

Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@scylladb.com>

syuu1228/seastar,avikivity/seastar,avikivity/seastar,scylladb/seastar,cloudius-systems/seastar,cloudius-systems/seastar,avikivity/seastar,syuu1228/seastar,scylladb/seastar,scylladb/seastar,cloudius-systems/seastar,syuu1228/seastar