engine: Dual mode shouldn't be sent to vdsm on hotplug nic

Since 3.0 vdsm doesn't support Dual mode on vm interface.
When running a vm, VmInfoBuilder takes care of replacing the
interface type in case it is Dual mode.
This patch adds the same treatment to hot plug nic.

Bug-Url: https://bugzilla.redhat.com/1079992
Bug-Url: https://bugzilla.redhat.com/1083959
Change-Id: Ifdc878a5f8391659a58cf25f2f9137c944689ce4
Signed-off-by: Alona Kaplan <alkaplan@redhat.com>