Add explicit cleanup to test_ports

Currently, resources are cleaned up as part of test class teardown.
The number of subnets this class creates has increased to the quota
maximum and no longer runs when tenant isolation is disabled unless
things get cleaned up per-test.

Also, this removes a duplicate test case.

Change-Id: Ica58eb8da471282f35ff7c05cafcb64d4fd73ba6
Closes-bug: #1411794
1 file changed