Collect current QoS settings for IO devices and report through RunningVmStats

This info will be used by mom when updating the IO limits and by engine
to report the current QoS settings to the user.

Change-Id: Ie4fab132b60ce6ae2285115034f3d1ffcdca9e9d
Signed-off-by: Martin Sivak <msivak@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/28712
Reviewed-by: Michal Skrivanek <michal.skrivanek@redhat.com>
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Francesco Romani <fromani@redhat.com>