engine: Spice cannot start if domain is null

Vm.getVmHost() return null for host name if the VmInit is null.

Bug-Url: https://bugzilla.redhat.com/1051041
Change-Id: I556150281d7d4417fff1dc9590a011baf6c17207
Signed-off-by: Shahar Havivi <shavivi@redhat.com>