core: Use the cluster emulated machine to run a VM

According to http://www.ovirt.org/Cluster_emulation_modes#Run%20VM

Instead of a global config value, use the cluster emulated machine
field.

Deleted the deprecated emulatedMachine Config value

Bug-Url: https://bugzilla.redhat.com/927874
Change-Id: I23736fcc1748e47ce82b84d5167c18dc370bd3ad
Signed-off-by: Roy Golan <rgolan@redhat.com>