core: saving the cpu_name in vm_dynamic

This patch adds the cpu_name property to the vm_dynamic table, to allow
knowing what cpu was configured in the cluster when running the VM

Change-Id: I2f13891b3425e4864334851ecb12d1d61a162082
Bug-Url: https://bugzilla.redhat.com/1006209
Signed-off-by: Oved Ourfali <oourfali@redhat.com>