monitor: add poll-* properties into query-iothreads result

IOthreads were recently extended by new properties that can
enable/disable and configure aio polling.  This will also allow
other tools that uses QEMU to probe for existence of those new
properties via query-qmp-schema.

Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Message-Id: <3163c16d6ab4257f7be9ad44fe9cc0ce8c359e5a.1486718555.git.phrdina@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>