Starting the macvtap agent without specifying at least one
physical_interface_mappings does not make sense. As it only
supports layer2 networks (flat, vlan) an interface mapping is
mandatory. An existing agent deployment without an interface
mapping can not serve any networks to instances!
This patch terminates the agent when no mapping is
provided. As without this mapping the agent cannot serve any networks
for instances, this patch can't really break existing deployments.
UpgradeImpact Agent terminates when no physical_interface_mapping
configuration is provided.
Change-Id: I647cf4da55fda54e32b7047b84e0d7f671629fa7
Closes-Bug: #1587444
