core: Push ioTune QoS info when hotplugging disk

This adds the support for disk QoS for disks that are hotplugged
while the VM is already running.

Change-Id: Ic4bb85cd307089088be77cff28adbc783ebcaedd
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1145665
Signed-off-by: Martin Sivák <msivak@redhat.com>