iotune: provide a status dump if we can't calculate a proper number of io_queues
iotune: provide a status dump if we can't calculate a proper number of io_queues

I have recently fixed a bug that happened because we have calculated the sweet
spot for concurrency to be 0. That same thing happened again in another
circumnstance.

The biggest problem is that by the time we find this (through a SIGFPE), the
object that deals with all the estimation is already destroyed and debugging
becomes very hard. I have some ideas about why is it that this is happening in
this case, but without hard data I may be aiming at the wrong thing.

This patch moves a sanity check test closer to the point where the problem first
happens. In itself, it makes it easier to analyze core dumps because the object
will be alive still. But since we're here, it also prints various relevant parts
of the internal state so debugging issues like that becomes easier.

Signed-off-by: Glauber Costa <7ba9037b0dd006f9408bd45b94707becd5cd4e87@scylladb.com>
Message-Id: <1467296381-30597-1-git-send-email-7ba9037b0dd006f9408bd45b94707becd5cd4e87@scylladb.com>

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