Make router func tests less racey
Make router func tests less racey

Some tests were sharing the same code that created a subnet.
This could cause problems if the tests were to run concurrently.
Avoid that by making each test specify the subnet CIDR it wants.

Change-Id: I0a4f8913af8f8069fc86f168cda35495553aee09

openstack-infra/shade,stackforge/python-openstacksdk,dtroyer/python-openstacksdk,openstack/python-openstacksdk,openstack/python-openstacksdk,dtroyer/python-openstacksdk,openstack-infra/shade,stackforge/python-openstacksdk