tests: fair_queue_perf: Switch on shared groups
tests: fair_queue_perf: Switch on shared groups

Once queues are strictly per-shard it makes no sense to measure the
performance of submitting a request to foreing queue. Instead, compare
the performance of queue with its own private groups vs node-wide group
that's shared by all shards' queues.

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

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