trunk: Create vxlan network when testing inherit

The inherit segmentation type fails only when parent network has a not
supported network type. In case default is a supported one, e.g. vlan,
then inherit correctly returns vlan as subport segmentation type.

This patch forces to use vxlan as a network type for test validating
inherit option.

Change-Id: Idf6935e4da426ff50457483a8f08a9ae3e403f75
Closes-bug: #1739227
2 files changed