core: HA Vm reservation check failure event log is not well resolved

Making the event log message more user readable,
using the host name and not the toString.

Change-Id: I245f8eea3a955bcd8e75c574c572cf2608452d68
Bug-Url: https://bugzilla.redhat.com/1057584
Signed-off-by: Kobi Ianko <kobi@redhat.com>