properly configure I/O Scheduler when --max-io-requests is passed
properly configure I/O Scheduler when --max-io-requests is passed

We now have scaling between reads and writes as part of the new I/O
Scheduler. However, when a capacity is explicitly set, which means the
old --max-io-requests is used, we end up miscalculating that, and as a
result the I/O Scheduler fails to uphold the shares.

If we are using the legacy config, which didn't differentiate reads from
writes, then we should hard code the ratio to 1.

Fixes #482

Signed-off-by: Glauber Costa <7ba9037b0dd006f9408bd45b94707becd5cd4e87@scylladb.com>
Message-Id: <20180808174029.12521-4-7ba9037b0dd006f9408bd45b94707becd5cd4e87@scylladb.com>

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