Remove invalid or useless initialization in test_type_vxlan

In test_type_vxlan, vni_ranges option is overriden with an invalid and unused
value, vxlan_group is overrriden but never used.

Change-Id: Ie1ce1d7a8ef54692d122276e371ec5efc2e68d9c
Merge "Remove invalid or useless initialization in test_type_vxlan"