If there are IOThread polling values in the query-iothreads return
buffer, then fill them in and set a bool indicating their presence.
This will allow for displaying in a domain stats output eventually.

Note that the QEMU values are managed a bit differently (as int's
stored in int64_t's) than we will manage them (as unsigned long and
int values). This is intentional to allow for value validation
checking when it comes time to provide the values to QEMU.
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>
ACKed-by: NMichal Privoznik <mprivozn@redhat.com>