core: disk_image_dynamic statistics (#892596)

vdsm sends disk statistics per disk, while disk_image_dynamic table
contains disk_image ids (volumes). Hence the update on disk ids that
VdsUpdateRunTimeInfo generates, actually does nothing. A quick fix for
this problem is that VdsUpdateRunTimeInfo now updates by the AI id, so
statistics are saved.

Change-Id: I9f49238e3a725184ad2feb2d5ff06996e462d377
Bug-Url: https://bugzilla.redhat.com/892596
Signed-off-by: Vered Volansky <vvolansk@redhat.com>