Support configuration of name or uuid (instead of only uuid) for 4 nsx_v3
parameters: default_overlay_tz, default_vlan_tz, default_bridge_cluster
and default_tier0_router.
Assert on init if the uuid or name was no found on the backend, or if the
name is not unique.
DocImpact: Configuration options default_overlay_tz_uuid, default_vlan_tz_uuid,
default_bridge_cluster_uuid and default_tier0_router_uuid were
replaced with default_overlay_tz, default_vlan_tz, default_bridge_cluster
and default_tier0_router and support name or uuid now.
Change-Id: Id153d4d69165b161c04c403b578657c51af20e9c
a88b99b6c9