Avoid default quota limit of 10 subnets

This test class only fails with no tenant isolation in the gate. The only
reason I can think of for this is that the non-isolated demo tenant has
an extra subnet created by devstack whereas the isolated tenant for this
test class does not. I tried putting addCleanups for the network and subnets
in the for loop but that caused other strange problems.

Change-Id: Ib86d54ee4cf317bb9d93d28fd62f44d738b5efaa
1 file changed