rl-iotest.py: Support recent changes in io_tester
rl-iotest.py: Support recent changes in io_tester

Add the ability to configure numbers fibers and shares for read
and write jobs as well as select sleeper type and distribution.

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

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