io_tester: Prepare for IO submission with intent
io_tester: Prepare for IO submission with intent

The rate-based requests sumission will send requests and
forget their futures. On stop it will cancel all in-flight
activity.

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

scylladb/seastar,avikivity/seastar,avikivity/seastar,syuu1228/seastar,scylladb/seastar,scylladb/seastar,syuu1228/seastar,avikivity/seastar,syuu1228/seastar