engine: Support interface QoS override in Setup Networks

Modified the Setup Networks command to also account for QoS override
on the host interface level. If the feature is supported and the QoS
entities are valid, the overridden QoS is persisted and passed to
VDSM.

Change-Id: I22a4fefac1c5e80c98a72507623152ea4d30ef07
Signed-off-by: Lior Vernia <lvernia@redhat.com>